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	$54.44	13.401%	$61.7355	$61.74	$61.75	$61.70
Purchase #2	$233.55	7.217%	$250.4053	$250.41	$250.40	$250.40
Purchase #3	$83.47	7.778%	$89.9623	$89.96	$89.95	$90.00
Purchase #4	$103.36	7.545%	$111.1585	$111.16	$111.15	$111.20
Purchase #5	$48.44	3.575%	$50.1717	$50.17	$50.15	$50.20
Purchase #6	$13.75	9.256%	$15.0227	$15.02	$15.00	$15.00
Purchase #7	$77.95	3.434%	$80.6268	$80.63	$80.65	$80.60
7 purchase totals =	$614.96		$659.0828	$659.09	$659.05	$659.10