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	$81.48	11.461%	$90.8184	$90.82	$90.80	$90.80
Purchase #2	$185.83	10.767%	$205.8383	$205.84	$205.85	$205.80
Purchase #3	$139.91	10.725%	$154.9153	$154.92	$154.90	$154.90
Purchase #4	$158.50	13.554%	$179.9831	$179.98	$180.00	$180.00
Purchase #5	$54.89	7.125%	$58.8009	$58.80	$58.80	$58.80
Purchase #6	$192.66	3.505%	$199.4127	$199.41	$199.40	$199.40
Purchase #7	$135.61	11.637%	$151.3909	$151.39	$151.40	$151.40
7 purchase totals =	$948.88		$1,041.1596	$1,041.16	$1,041.15	$1,041.10