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	$200.40	4.596%	$209.6104	$209.61	$209.60	$209.60
Purchase #2	$231.59	9.601%	$253.825	$253.83	$253.85	$253.80
Purchase #3	$142.75	9.761%	$156.6838	$156.68	$156.70	$156.70
Purchase #4	$114.52	3.186%	$118.1686	$118.17	$118.15	$118.20
Purchase #5	$9.40	12.266%	$10.553	$10.55	$10.55	$10.60
Purchase #6	$48.73	10.584%	$53.8876	$53.89	$53.90	$53.90
Purchase #7	$97.33	9.538%	$106.6133	$106.61	$106.60	$106.60
7 purchase totals =	$844.72		$909.3417	$909.34	$909.35	$909.40