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	$45.90	9.626%	$50.3183	$50.32	$50.30	$50.30
Purchase #2	$83.58	10.142%	$92.0567	$92.06	$92.05	$92.10
Purchase #3	$13.37	10.390%	$14.7591	$14.76	$14.75	$14.80
Purchase #4	$188.52	5.727%	$199.3165	$199.32	$199.30	$199.30
Purchase #5	$28.77	12.413%	$32.3412	$32.34	$32.35	$32.30
Purchase #6	$62.82	13.750%	$71.4578	$71.46	$71.45	$71.50
Purchase #7	$12.89	7.426%	$13.8472	$13.85	$13.85	$13.80
7 purchase totals =	$435.85		$474.0968	$474.11	$474.05	$474.10