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	$30.82	7.642%	$33.1753	$33.18	$33.20	$33.20
Purchase #2	$218.52	13.429%	$247.8651	$247.87	$247.85	$247.90
Purchase #3	$93.70	5.162%	$98.5368	$98.54	$98.55	$98.50
Purchase #4	$122.77	6.517%	$130.7709	$130.77	$130.75	$130.80
Purchase #5	$61.60	10.218%	$67.8943	$67.89	$67.90	$67.90
Purchase #6	$86.36	3.256%	$89.1719	$89.17	$89.15	$89.20
Purchase #7	$225.51	9.346%	$246.5862	$246.59	$246.60	$246.60
7 purchase totals =	$839.28		$914.0005	$914.01	$914.00	$914.10