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	$11.80	4.331%	$12.3111	$12.31	$12.30	$12.30
Purchase #2	$89.92	12.121%	$100.8192	$100.82	$100.80	$100.80
Purchase #3	$231.89	7.857%	$250.1096	$250.11	$250.10	$250.10
Purchase #4	$54.39	5.145%	$57.1884	$57.19	$57.20	$57.20
Purchase #5	$202.90	10.339%	$223.8778	$223.88	$223.90	$223.90
Purchase #6	$203.90	6.811%	$217.7876	$217.79	$217.80	$217.80
Purchase #7	$122.49	4.707%	$128.2556	$128.26	$128.25	$128.30
7 purchase totals =	$917.29		$990.3493	$990.36	$990.35	$990.40