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	$48.47	12.630%	$54.5918	$54.59	$54.60	$54.60
Purchase #2	$85.92	3.287%	$88.7442	$88.74	$88.75	$88.70
Purchase #3	$127.42	12.591%	$143.4635	$143.46	$143.45	$143.50
Purchase #4	$176.46	10.349%	$194.7218	$194.72	$194.70	$194.70
Purchase #5	$124.75	9.687%	$136.8345	$136.83	$136.85	$136.80
Purchase #6	$80.53	3.819%	$83.6054	$83.61	$83.60	$83.60
Purchase #7	$36.85	5.518%	$38.8834	$38.88	$38.90	$38.90
7 purchase totals =	$680.40		$740.8446	$740.83	$740.85	$740.80