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	$250.91	7.546%	$269.8437	$269.84	$269.85	$269.80
Purchase #2	$246.71	11.341%	$274.6894	$274.69	$274.70	$274.70
Purchase #3	$75.47	3.825%	$78.3567	$78.36	$78.35	$78.40
Purchase #4	$30.57	10.333%	$33.7288	$33.73	$33.75	$33.70
Purchase #5	$10.94	8.333%	$11.8516	$11.85	$11.85	$11.90
Purchase #6	$214.57	3.840%	$222.8095	$222.81	$222.80	$222.80
Purchase #7	$29.94	10.547%	$33.0978	$33.10	$33.10	$33.10
7 purchase totals =	$859.11		$924.3775	$924.38	$924.40	$924.40