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	$40.44	4.485%	$42.2537	$42.25	$42.25	$42.30
Purchase #2	$250.40	13.727%	$284.7724	$284.77	$284.75	$284.80
Purchase #3	$152.86	9.454%	$167.3114	$167.31	$167.30	$167.30
Purchase #4	$193.90	3.128%	$199.9652	$199.97	$199.95	$200.00
Purchase #5	$55.33	11.268%	$61.5646	$61.56	$61.55	$61.60
Purchase #6	$57.59	12.433%	$64.7502	$64.75	$64.75	$64.80
Purchase #7	$128.72	5.685%	$136.0377	$136.04	$136.05	$136.00
7 purchase totals =	$879.24		$956.6552	$956.65	$956.60	$956.80