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	$74.62	12.344%	$83.8311	$83.83	$83.85	$83.80
Purchase #2	$143.41	7.169%	$153.6911	$153.69	$153.70	$153.70
Purchase #3	$57.31	4.648%	$59.9738	$59.97	$59.95	$60.00
Purchase #4	$65.67	10.754%	$72.7322	$72.73	$72.75	$72.70
Purchase #5	$70.55	11.546%	$78.6957	$78.70	$78.70	$78.70
Purchase #6	$83.47	7.846%	$90.0191	$90.02	$90.00	$90.00
Purchase #7	$112.72	10.719%	$124.8025	$124.80	$124.80	$124.80
7 purchase totals =	$607.75		$663.7455	$663.74	$663.75	$663.70