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	$234.76	4.182%	$244.5777	$244.58	$244.60	$244.60
Purchase #2	$248.42	10.864%	$275.4083	$275.41	$275.40	$275.40
Purchase #3	$138.92	13.689%	$157.9368	$157.94	$157.95	$157.90
Purchase #4	$102.46	12.797%	$115.5718	$115.57	$115.55	$115.60
Purchase #5	$132.65	13.776%	$150.9239	$150.92	$150.90	$150.90
Purchase #6	$125.84	6.410%	$133.9063	$133.91	$133.90	$133.90
Purchase #7	$226.34	13.332%	$256.5156	$256.52	$256.50	$256.50
7 purchase totals =	$1,209.39		$1,334.8404	$1,334.85	$1,334.80	$1,334.80