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	$37.51	12.338%	$42.138	$42.14	$42.15	$42.10
Purchase #2	$226.46	7.698%	$243.8929	$243.89	$243.90	$243.90
Purchase #3	$233.91	12.665%	$263.5347	$263.53	$263.55	$263.50
Purchase #4	$185.52	11.397%	$206.6637	$206.66	$206.65	$206.70
Purchase #5	$232.83	10.200%	$256.5787	$256.58	$256.60	$256.60
Purchase #6	$47.80	10.335%	$52.7401	$52.74	$52.75	$52.70
Purchase #7	$16.52	12.336%	$18.5579	$18.56	$18.55	$18.60
7 purchase totals =	$980.55		$1,084.1060	$1,084.10	$1,084.15	$1,084.10