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	$89.27	12.636%	$100.5502	$100.55	$100.55	$100.60
Purchase #2	$88.94	13.164%	$100.6481	$100.65	$100.65	$100.60
Purchase #3	$140.69	13.622%	$159.8548	$159.85	$159.85	$159.90
Purchase #4	$20.48	13.305%	$23.2049	$23.20	$23.20	$23.20
Purchase #5	$244.33	13.172%	$276.5131	$276.51	$276.50	$276.50
Purchase #6	$246.30	6.505%	$262.3218	$262.32	$262.30	$262.30
Purchase #7	$13.74	9.405%	$15.0322	$15.03	$15.05	$15.00
7 purchase totals =	$843.75		$938.1251	$938.11	$938.10	$938.10