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	$143.80	10.738%	$159.2412	$159.24	$159.25	$159.20
Purchase #2	$67.91	5.343%	$71.5384	$71.54	$71.55	$71.50
Purchase #3	$35.68	11.563%	$39.8057	$39.81	$39.80	$39.80
Purchase #4	$105.53	3.725%	$109.461	$109.46	$109.45	$109.50
Purchase #5	$195.81	9.557%	$214.5236	$214.52	$214.50	$214.50
Purchase #6	$218.30	4.825%	$228.833	$228.83	$228.85	$228.80
Purchase #7	$11.58	8.168%	$12.5259	$12.53	$12.55	$12.50
7 purchase totals =	$778.61		$835.9288	$835.93	$835.95	$835.80