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	$185.59	13.133%	$209.9635	$209.96	$209.95	$210.00
Purchase #2	$73.63	12.151%	$82.5768	$82.58	$82.60	$82.60
Purchase #3	$159.83	12.568%	$179.9174	$179.92	$179.90	$179.90
Purchase #4	$119.99	4.143%	$124.9612	$124.96	$124.95	$125.00
Purchase #5	$111.57	5.559%	$117.7722	$117.77	$117.75	$117.80
Purchase #6	$234.25	7.103%	$250.8888	$250.89	$250.90	$250.90
Purchase #7	$7.40	4.530%	$7.7352	$7.74	$7.75	$7.70
7 purchase totals =	$892.26		$973.8151	$973.82	$973.80	$973.90