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	$235.95	4.323%	$246.1501	$246.15	$246.15	$246.20
Purchase #2	$83.30	6.638%	$88.8295	$88.83	$88.85	$88.80
Purchase #3	$105.90	7.179%	$113.5026	$113.50	$113.50	$113.50
Purchase #4	$32.99	13.524%	$37.4516	$37.45	$37.45	$37.50
Purchase #5	$249.82	10.372%	$275.7313	$275.73	$275.75	$275.70
Purchase #6	$45.48	11.178%	$50.5638	$50.56	$50.55	$50.60
Purchase #7	$237.28	11.388%	$264.3014	$264.30	$264.30	$264.30
7 purchase totals =	$990.72		$1,076.5303	$1,076.52	$1,076.55	$1,076.60