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	$121.52	12.648%	$136.8898	$136.89	$136.90	$136.90
Purchase #2	$99.35	12.114%	$111.3853	$111.39	$111.40	$111.40
Purchase #3	$21.83	13.340%	$24.7421	$24.74	$24.75	$24.70
Purchase #4	$215.67	11.818%	$241.1579	$241.16	$241.15	$241.20
Purchase #5	$104.43	10.602%	$115.5017	$115.50	$115.50	$115.50
Purchase #6	$141.87	13.380%	$160.8522	$160.85	$160.85	$160.90
Purchase #7	$110.51	13.629%	$125.5714	$125.57	$125.55	$125.60
7 purchase totals =	$815.18		$916.1004	$916.10	$916.10	$916.20