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	$223.42	12.573%	$251.5106	$251.51	$251.50	$251.50
Purchase #2	$247.84	6.126%	$263.0227	$263.02	$263.00	$263.00
Purchase #3	$120.81	13.788%	$137.4673	$137.47	$137.45	$137.50
Purchase #4	$199.40	11.720%	$222.7697	$222.77	$222.75	$222.80
Purchase #5	$35.85	4.419%	$37.4342	$37.43	$37.45	$37.40
Purchase #6	$120.69	6.420%	$128.4383	$128.44	$128.45	$128.40
Purchase #7	$56.48	9.431%	$61.8066	$61.81	$61.80	$61.80
7 purchase totals =	$1,004.49		$1,102.4494	$1,102.45	$1,102.40	$1,102.40