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	$222.97	12.319%	$250.4377	$250.44	$250.45	$250.40
Purchase #2	$247.42	4.252%	$257.9403	$257.94	$257.95	$257.90
Purchase #3	$122.25	4.244%	$127.4383	$127.44	$127.45	$127.40
Purchase #4	$59.62	10.372%	$65.8038	$65.80	$65.80	$65.80
Purchase #5	$92.69	13.134%	$104.8639	$104.86	$104.85	$104.90
Purchase #6	$59.48	8.669%	$64.6363	$64.64	$64.65	$64.60
Purchase #7	$30.59	10.541%	$33.8145	$33.81	$33.80	$33.80
7 purchase totals =	$835.02		$904.9348	$904.93	$904.95	$904.80