Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$35.48	8.536%	$38.5086	$38.51	$38.50	$38.50
Purchase #2	$90.90	13.717%	$103.3688	$103.37	$103.35	$103.40
Purchase #3	$165.52	8.423%	$179.4617	$179.46	$179.45	$179.50
Purchase #4	$169.43	3.653%	$175.6193	$175.62	$175.60	$175.60
Purchase #5	$171.99	9.589%	$188.4821	$188.48	$188.50	$188.50
Purchase #6	$42.61	3.107%	$43.9339	$43.93	$43.95	$43.90
Purchase #7	$72.88	4.839%	$76.4067	$76.41	$76.40	$76.40
7 purchase totals =	$748.81		$805.7811	$805.78	$805.75	$805.80