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	$128.31	4.139%	$133.6208	$133.62	$133.60	$133.60
Purchase #2	$98.96	5.405%	$104.3088	$104.31	$104.30	$104.30
Purchase #3	$187.28	9.726%	$205.4949	$205.49	$205.50	$205.50
Purchase #4	$37.61	3.131%	$38.7876	$38.79	$38.80	$38.80
Purchase #5	$189.96	5.718%	$200.8219	$200.82	$200.80	$200.80
Purchase #6	$72.78	9.478%	$79.6781	$79.68	$79.70	$79.70
Purchase #7	$222.35	4.157%	$231.5931	$231.59	$231.60	$231.60
7 purchase totals =	$937.25		$994.3052	$994.30	$994.30	$994.30