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	$136.75	10.315%	$150.8558	$150.86	$150.85	$150.90
Purchase #2	$35.83	13.218%	$40.566	$40.57	$40.55	$40.60
Purchase #3	$226.67	10.413%	$250.2731	$250.27	$250.25	$250.30
Purchase #4	$19.40	9.840%	$21.309	$21.31	$21.30	$21.30
Purchase #5	$58.54	13.535%	$66.4634	$66.46	$66.45	$66.50
Purchase #6	$139.56	11.520%	$155.6373	$155.64	$155.65	$155.60
Purchase #7	$84.69	12.492%	$95.2695	$95.27	$95.25	$95.30
7 purchase totals =	$701.44		$780.3741	$780.38	$780.30	$780.50