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	$203.74	9.407%	$222.9058	$222.91	$222.90	$222.90
Purchase #2	$240.94	5.145%	$253.3364	$253.34	$253.35	$253.30
Purchase #3	$93.49	10.539%	$103.3429	$103.34	$103.35	$103.30
Purchase #4	$235.59	4.796%	$246.8889	$246.89	$246.90	$246.90
Purchase #5	$152.98	12.662%	$172.3503	$172.35	$172.35	$172.40
Purchase #6	$61.63	5.242%	$64.8606	$64.86	$64.85	$64.90
Purchase #7	$199.81	13.344%	$226.4726	$226.47	$226.45	$226.50
7 purchase totals =	$1,188.18		$1,290.1575	$1,290.16	$1,290.15	$1,290.20