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	$84.79	7.288%	$90.9695	$90.97	$90.95	$91.00
Purchase #2	$197.54	9.166%	$215.6465	$215.65	$215.65	$215.60
Purchase #3	$35.33	5.339%	$37.2163	$37.22	$37.20	$37.20
Purchase #4	$239.89	5.715%	$253.5997	$253.60	$253.60	$253.60
Purchase #5	$173.43	12.850%	$195.7158	$195.72	$195.70	$195.70
Purchase #6	$132.66	8.814%	$144.3527	$144.35	$144.35	$144.40
Purchase #7	$139.77	13.672%	$158.8794	$158.88	$158.90	$158.90
7 purchase totals =	$1,003.41		$1,096.3799	$1,096.39	$1,096.35	$1,096.40