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	$45.62	12.172%	$51.1729	$51.17	$51.15	$51.20
Purchase #2	$77.95	7.362%	$83.6887	$83.69	$83.70	$83.70
Purchase #3	$250.79	3.596%	$259.8084	$259.81	$259.80	$259.80
Purchase #4	$37.50	7.590%	$40.3463	$40.35	$40.35	$40.30
Purchase #5	$117.44	12.297%	$131.8816	$131.88	$131.90	$131.90
Purchase #6	$149.92	3.318%	$154.8943	$154.89	$154.90	$154.90
Purchase #7	$247.85	3.507%	$256.5421	$256.54	$256.55	$256.50
7 purchase totals =	$927.07		$978.3343	$978.33	$978.35	$978.30