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	$87.55	3.775%	$90.855	$90.86	$90.85	$90.90
Purchase #2	$218.63	6.172%	$232.1238	$232.12	$232.10	$232.10
Purchase #3	$243.86	13.861%	$277.6614	$277.66	$277.65	$277.70
Purchase #4	$149.45	11.340%	$166.3976	$166.40	$166.40	$166.40
Purchase #5	$224.93	3.589%	$233.0027	$233.00	$233.00	$233.00
Purchase #6	$203.90	7.631%	$219.4596	$219.46	$219.45	$219.50
Purchase #7	$171.72	11.530%	$191.5193	$191.52	$191.50	$191.50
7 purchase totals =	$1,300.04		$1,411.0194	$1,411.02	$1,410.95	$1,411.10