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	$232.79	12.184%	$261.1531	$261.15	$261.15	$261.20
Purchase #2	$36.69	9.130%	$40.0398	$40.04	$40.05	$40.00
Purchase #3	$223.35	13.298%	$253.0511	$253.05	$253.05	$253.10
Purchase #4	$48.25	12.381%	$54.2238	$54.22	$54.20	$54.20
Purchase #5	$152.25	8.342%	$164.9507	$164.95	$164.95	$165.00
Purchase #6	$167.64	10.279%	$184.8717	$184.87	$184.85	$184.90
Purchase #7	$117.85	10.846%	$130.632	$130.63	$130.65	$130.60
7 purchase totals =	$978.82		$1,088.9222	$1,088.91	$1,088.90	$1,089.00