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	$6.77	5.695%	$7.1556	$7.16	$7.15	$7.20
Purchase #2	$216.37	3.556%	$224.0641	$224.06	$224.05	$224.10
Purchase #3	$19.26	12.483%	$21.6642	$21.66	$21.65	$21.70
Purchase #4	$230.25	8.367%	$249.515	$249.52	$249.50	$249.50
Purchase #5	$102.86	8.375%	$111.4745	$111.47	$111.45	$111.50
Purchase #6	$239.97	9.535%	$262.8511	$262.85	$262.85	$262.90
Purchase #7	$114.30	10.157%	$125.9095	$125.91	$125.90	$125.90
7 purchase totals =	$929.78		$1,002.6340	$1,002.63	$1,002.55	$1,002.80