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	$115.42	11.287%	$128.4475	$128.45	$128.45	$128.40
Purchase #2	$243.43	12.737%	$274.4357	$274.44	$274.45	$274.40
Purchase #3	$44.52	4.829%	$46.6699	$46.67	$46.65	$46.70
Purchase #4	$210.39	5.473%	$221.9046	$221.90	$221.90	$221.90
Purchase #5	$75.51	12.633%	$85.0492	$85.05	$85.05	$85.00
Purchase #6	$54.72	8.686%	$59.473	$59.47	$59.45	$59.50
Purchase #7	$37.45	4.319%	$39.0675	$39.07	$39.05	$39.10
7 purchase totals =	$781.44		$855.0474	$855.05	$855.00	$855.00