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	$55.29	12.150%	$62.0077	$62.01	$62.00	$62.00
Purchase #2	$61.68	13.864%	$70.2313	$70.23	$70.25	$70.20
Purchase #3	$66.92	6.579%	$71.3227	$71.32	$71.30	$71.30
Purchase #4	$207.82	7.654%	$223.7265	$223.73	$223.75	$223.70
Purchase #5	$18.81	9.816%	$20.6564	$20.66	$20.65	$20.70
Purchase #6	$20.80	11.660%	$23.2253	$23.23	$23.25	$23.20
Purchase #7	$30.41	7.585%	$32.7166	$32.72	$32.70	$32.70
7 purchase totals =	$461.73		$503.8865	$503.90	$503.90	$503.80