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	$125.43	6.297%	$133.3283	$133.33	$133.35	$133.30
Purchase #2	$34.59	9.549%	$37.893	$37.89	$37.90	$37.90
Purchase #3	$185.45	10.485%	$204.8944	$204.89	$204.90	$204.90
Purchase #4	$46.64	9.842%	$51.2303	$51.23	$51.25	$51.20
Purchase #5	$6.85	3.754%	$7.1071	$7.11	$7.10	$7.10
Purchase #6	$117.47	4.170%	$122.3685	$122.37	$122.35	$122.40
Purchase #7	$97.29	12.851%	$109.7927	$109.79	$109.80	$109.80
7 purchase totals =	$613.72		$666.6143	$666.61	$666.65	$666.60