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	$35.80	12.562%	$40.2972	$40.30	$40.30	$40.30
Purchase #2	$122.28	7.795%	$131.8117	$131.81	$131.80	$131.80
Purchase #3	$39.93	13.559%	$45.3441	$45.34	$45.35	$45.30
Purchase #4	$145.75	9.423%	$159.484	$159.48	$159.50	$159.50
Purchase #5	$227.30	3.467%	$235.1805	$235.18	$235.20	$235.20
Purchase #6	$223.54	13.418%	$253.5346	$253.53	$253.55	$253.50
Purchase #7	$10.78	4.448%	$11.2595	$11.26	$11.25	$11.30
7 purchase totals =	$805.38		$876.9116	$876.90	$876.95	$876.90