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	$33.41	10.143%	$36.7988	$36.80	$36.80	$36.80
Purchase #2	$97.38	13.597%	$110.6208	$110.62	$110.60	$110.60
Purchase #3	$66.89	7.248%	$71.7382	$71.74	$71.75	$71.70
Purchase #4	$86.92	3.444%	$89.9135	$89.91	$89.90	$89.90
Purchase #5	$161.32	6.694%	$172.1188	$172.12	$172.10	$172.10
Purchase #6	$67.58	7.213%	$72.4545	$72.45	$72.45	$72.50
Purchase #7	$85.38	9.308%	$93.3272	$93.33	$93.35	$93.30
7 purchase totals =	$598.88		$646.9718	$646.97	$646.95	$646.90