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	$154.53	11.170%	$171.791	$171.79	$171.80	$171.80
Purchase #2	$236.73	10.468%	$261.5109	$261.51	$261.50	$261.50
Purchase #3	$216.85	7.519%	$233.155	$233.16	$233.15	$233.20
Purchase #4	$210.81	6.415%	$224.3335	$224.33	$224.35	$224.30
Purchase #5	$230.66	12.252%	$258.9205	$258.92	$258.90	$258.90
Purchase #6	$154.75	3.358%	$159.9465	$159.95	$159.95	$159.90
Purchase #7	$179.89	11.453%	$200.4928	$200.49	$200.50	$200.50
7 purchase totals =	$1,384.22		$1,510.1502	$1,510.15	$1,510.15	$1,510.10