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	$243.92	11.164%	$271.1512	$271.15	$271.15	$271.20
Purchase #2	$225.59	11.313%	$251.111	$251.11	$251.10	$251.10
Purchase #3	$190.93	12.321%	$214.4545	$214.45	$214.45	$214.50
Purchase #4	$247.86	8.674%	$269.3594	$269.36	$269.35	$269.40
Purchase #5	$9.66	4.441%	$10.089	$10.09	$10.10	$10.10
Purchase #6	$45.85	10.115%	$50.4877	$50.49	$50.50	$50.50
Purchase #7	$62.39	4.548%	$65.2275	$65.23	$65.25	$65.20
7 purchase totals =	$1,026.20		$1,131.8803	$1,131.88	$1,131.90	$1,132.00