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	$124.27	7.717%	$133.8599	$133.86	$133.85	$133.90
Purchase #2	$61.54	4.872%	$64.5382	$64.54	$64.55	$64.50
Purchase #3	$157.84	6.378%	$167.907	$167.91	$167.90	$167.90
Purchase #4	$184.52	8.340%	$199.909	$199.91	$199.90	$199.90
Purchase #5	$38.78	3.400%	$40.0985	$40.10	$40.10	$40.10
Purchase #6	$87.94	13.620%	$99.9174	$99.92	$99.90	$99.90
Purchase #7	$242.42	3.791%	$251.6101	$251.61	$251.60	$251.60
7 purchase totals =	$897.31		$957.8401	$957.85	$957.80	$957.80