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	$36.45	3.530%	$37.7367	$37.74	$37.75	$37.70
Purchase #2	$54.77	8.165%	$59.242	$59.24	$59.25	$59.20
Purchase #3	$42.55	10.282%	$46.925	$46.93	$46.95	$46.90
Purchase #4	$175.25	5.151%	$184.2771	$184.28	$184.30	$184.30
Purchase #5	$120.69	10.287%	$133.1054	$133.11	$133.10	$133.10
Purchase #6	$188.43	12.625%	$212.2193	$212.22	$212.20	$212.20
Purchase #7	$160.37	13.774%	$182.4594	$182.46	$182.45	$182.50
7 purchase totals =	$778.51		$855.9649	$855.98	$856.00	$855.90