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	$137.85	3.161%	$142.2074	$142.21	$142.20	$142.20
Purchase #2	$130.75	8.332%	$141.6441	$141.64	$141.65	$141.60
Purchase #3	$225.50	13.689%	$256.3687	$256.37	$256.35	$256.40
Purchase #4	$120.72	8.112%	$130.5128	$130.51	$130.50	$130.50
Purchase #5	$145.68	4.470%	$152.1919	$152.19	$152.20	$152.20
Purchase #6	$64.57	4.772%	$67.6513	$67.65	$67.65	$67.70
Purchase #7	$30.91	6.309%	$32.8601	$32.86	$32.85	$32.90
7 purchase totals =	$855.98		$923.4363	$923.43	$923.40	$923.50