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	$245.38	4.822%	$257.2122	$257.21	$257.20	$257.20
Purchase #2	$44.89	7.281%	$48.1584	$48.16	$48.15	$48.20
Purchase #3	$89.55	11.485%	$99.8348	$99.83	$99.85	$99.80
Purchase #4	$64.93	10.138%	$71.5126	$71.51	$71.50	$71.50
Purchase #5	$37.71	13.601%	$42.8389	$42.84	$42.85	$42.80
Purchase #6	$171.86	7.624%	$184.9626	$184.96	$184.95	$185.00
Purchase #7	$179.59	13.190%	$203.2779	$203.28	$203.30	$203.30
7 purchase totals =	$833.91		$907.7974	$907.79	$907.80	$907.80