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	$245.34	12.248%	$275.3892	$275.39	$275.40	$275.40
Purchase #2	$88.93	4.287%	$92.7424	$92.74	$92.75	$92.70
Purchase #3	$210.54	12.602%	$237.0723	$237.07	$237.05	$237.10
Purchase #4	$207.73	12.593%	$233.8894	$233.89	$233.90	$233.90
Purchase #5	$163.39	9.833%	$179.4561	$179.46	$179.45	$179.50
Purchase #6	$6.82	8.753%	$7.417	$7.42	$7.40	$7.40
Purchase #7	$175.56	8.499%	$190.4808	$190.48	$190.50	$190.50
7 purchase totals =	$1,098.31		$1,216.4472	$1,216.45	$1,216.45	$1,216.50