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	$36.31	12.642%	$40.9003	$40.90	$40.90	$40.90
Purchase #2	$197.57	6.446%	$210.3054	$210.31	$210.30	$210.30
Purchase #3	$177.59	11.208%	$197.4943	$197.49	$197.50	$197.50
Purchase #4	$236.79	7.620%	$254.8334	$254.83	$254.85	$254.80
Purchase #5	$127.34	8.726%	$138.4517	$138.45	$138.45	$138.50
Purchase #6	$165.57	12.275%	$185.8937	$185.89	$185.90	$185.90
Purchase #7	$225.72	8.864%	$245.7278	$245.73	$245.75	$245.70
7 purchase totals =	$1,166.89		$1,273.6066	$1,273.60	$1,273.65	$1,273.60