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	$91.52	12.721%	$103.1623	$103.16	$103.15	$103.20
Purchase #2	$90.44	10.486%	$99.9235	$99.92	$99.90	$99.90
Purchase #3	$232.74	13.479%	$264.111	$264.11	$264.10	$264.10
Purchase #4	$57.64	12.331%	$64.7476	$64.75	$64.75	$64.70
Purchase #5	$151.51	9.267%	$165.5504	$165.55	$165.55	$165.60
Purchase #6	$227.91	9.224%	$248.9324	$248.93	$248.95	$248.90
Purchase #7	$124.77	12.839%	$140.7892	$140.79	$140.80	$140.80
7 purchase totals =	$976.53		$1,087.2164	$1,087.21	$1,087.20	$1,087.20