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	$236.42	5.644%	$249.7635	$249.76	$249.75	$249.80
Purchase #2	$208.85	11.846%	$233.5904	$233.59	$233.60	$233.60
Purchase #3	$133.88	13.195%	$151.5455	$151.55	$151.55	$151.50
Purchase #4	$222.91	4.520%	$232.9855	$232.99	$233.00	$233.00
Purchase #5	$26.85	9.370%	$29.3658	$29.37	$29.35	$29.40
Purchase #6	$91.60	8.641%	$99.5152	$99.52	$99.50	$99.50
Purchase #7	$99.43	13.192%	$112.5468	$112.55	$112.55	$112.50
7 purchase totals =	$1,019.94		$1,109.3127	$1,109.33	$1,109.30	$1,109.30