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	$123.47	5.526%	$130.293	$130.29	$130.30	$130.30
Purchase #2	$211.35	10.313%	$233.1465	$233.15	$233.15	$233.10
Purchase #3	$5.61	13.729%	$6.3802	$6.38	$6.40	$6.40
Purchase #4	$40.70	11.384%	$45.3333	$45.33	$45.35	$45.30
Purchase #5	$233.57	6.748%	$249.3313	$249.33	$249.35	$249.30
Purchase #6	$127.35	4.706%	$133.3431	$133.34	$133.35	$133.30
Purchase #7	$84.82	11.300%	$94.4047	$94.40	$94.40	$94.40
7 purchase totals =	$826.87		$892.2321	$892.22	$892.30	$892.10