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	$33.93	8.162%	$36.6994	$36.70	$36.70	$36.70
Purchase #2	$190.57	3.150%	$196.573	$196.57	$196.55	$196.60
Purchase #3	$72.30	9.157%	$78.9205	$78.92	$78.90	$78.90
Purchase #4	$236.38	4.583%	$247.2133	$247.21	$247.20	$247.20
Purchase #5	$143.90	6.427%	$153.1485	$153.15	$153.15	$153.10
Purchase #6	$117.72	4.330%	$122.8173	$122.82	$122.80	$122.80
Purchase #7	$206.68	6.679%	$220.4842	$220.48	$220.50	$220.50
7 purchase totals =	$1,001.48		$1,055.8562	$1,055.85	$1,055.80	$1,055.80