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	$75.38	13.130%	$85.2774	$85.28	$85.30	$85.30
Purchase #2	$34.38	12.344%	$38.6239	$38.62	$38.60	$38.60
Purchase #3	$223.65	13.255%	$253.2948	$253.29	$253.30	$253.30
Purchase #4	$39.29	9.700%	$43.1011	$43.10	$43.10	$43.10
Purchase #5	$177.38	4.427%	$185.2326	$185.23	$185.25	$185.20
Purchase #6	$109.27	4.791%	$114.5051	$114.51	$114.50	$114.50
Purchase #7	$215.29	9.519%	$235.7835	$235.78	$235.80	$235.80
7 purchase totals =	$874.64		$955.8184	$955.81	$955.85	$955.80