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	$120.62	3.302%	$124.6029	$124.60	$124.60	$124.60
Purchase #2	$125.82	8.851%	$136.9563	$136.96	$136.95	$137.00
Purchase #3	$11.82	11.788%	$13.2133	$13.21	$13.20	$13.20
Purchase #4	$89.56	7.329%	$96.1239	$96.12	$96.10	$96.10
Purchase #5	$49.98	9.123%	$54.5397	$54.54	$54.55	$54.50
Purchase #6	$57.43	7.639%	$61.8171	$61.82	$61.80	$61.80
Purchase #7	$137.36	12.486%	$154.5108	$154.51	$154.50	$154.50
7 purchase totals =	$592.59		$641.7640	$641.76	$641.70	$641.70