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	$92.35	11.428%	$102.9038	$102.90	$102.90	$102.90
Purchase #2	$11.82	10.872%	$13.1051	$13.11	$13.10	$13.10
Purchase #3	$180.40	8.588%	$195.8928	$195.89	$195.90	$195.90
Purchase #4	$121.32	5.267%	$127.7099	$127.71	$127.70	$127.70
Purchase #5	$18.27	6.339%	$19.4281	$19.43	$19.45	$19.40
Purchase #6	$59.75	5.252%	$62.8881	$62.89	$62.90	$62.90
Purchase #7	$56.56	9.871%	$62.143	$62.14	$62.15	$62.10
7 purchase totals =	$540.47		$584.0708	$584.07	$584.10	$584.00