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	$55.72	4.448%	$58.1984	$58.20	$58.20	$58.20
Purchase #2	$26.43	9.367%	$28.9057	$28.91	$28.90	$28.90
Purchase #3	$32.54	8.827%	$35.4123	$35.41	$35.40	$35.40
Purchase #4	$5.82	11.801%	$6.5068	$6.51	$6.50	$6.50
Purchase #5	$117.90	11.410%	$131.3524	$131.35	$131.35	$131.40
Purchase #6	$78.58	4.492%	$82.1098	$82.11	$82.10	$82.10
Purchase #7	$223.75	8.791%	$243.4199	$243.42	$243.40	$243.40
7 purchase totals =	$540.74		$585.9053	$585.91	$585.85	$585.90