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	$161.68	7.257%	$173.4131	$173.41	$173.40	$173.40
Purchase #2	$137.38	6.715%	$146.6051	$146.61	$146.60	$146.60
Purchase #3	$218.62	11.759%	$244.3275	$244.33	$244.35	$244.30
Purchase #4	$6.33	7.838%	$6.8261	$6.83	$6.85	$6.80
Purchase #5	$173.42	8.750%	$188.5943	$188.59	$188.60	$188.60
Purchase #6	$66.73	8.454%	$72.3714	$72.37	$72.35	$72.40
Purchase #7	$34.80	8.819%	$37.869	$37.87	$37.85	$37.90
7 purchase totals =	$798.96		$870.0065	$870.01	$870.00	$870.00