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	$35.59	3.386%	$36.7951	$36.80	$36.80	$36.80
Purchase #2	$165.80	13.525%	$188.2245	$188.22	$188.20	$188.20
Purchase #3	$221.71	3.246%	$228.9067	$228.91	$228.90	$228.90
Purchase #4	$86.58	4.726%	$90.6718	$90.67	$90.65	$90.70
Purchase #5	$102.44	3.351%	$105.8728	$105.87	$105.85	$105.90
Purchase #6	$75.55	3.575%	$78.2509	$78.25	$78.25	$78.30
Purchase #7	$190.79	13.198%	$215.9705	$215.97	$215.95	$216.00
7 purchase totals =	$878.46		$944.6923	$944.69	$944.60	$944.80