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	$77.47	4.634%	$81.06	$81.06	$81.05	$81.10
Purchase #2	$76.25	7.838%	$82.2265	$82.23	$82.25	$82.20
Purchase #3	$32.43	4.291%	$33.8216	$33.82	$33.80	$33.80
Purchase #4	$53.60	7.437%	$57.5862	$57.59	$57.60	$57.60
Purchase #5	$35.51	6.195%	$37.7098	$37.71	$37.70	$37.70
Purchase #6	$167.94	4.514%	$175.5208	$175.52	$175.50	$175.50
Purchase #7	$198.77	8.333%	$215.3335	$215.33	$215.35	$215.30
7 purchase totals =	$641.97		$683.2584	$683.26	$683.25	$683.20