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	$226.29	9.409%	$247.5816	$247.58	$247.60	$247.60
Purchase #2	$72.91	8.230%	$78.9105	$78.91	$78.90	$78.90
Purchase #3	$189.77	10.408%	$209.5213	$209.52	$209.50	$209.50
Purchase #4	$250.40	12.193%	$280.9313	$280.93	$280.95	$280.90
Purchase #5	$124.52	12.676%	$140.3042	$140.30	$140.30	$140.30
Purchase #6	$9.66	11.504%	$10.7713	$10.77	$10.75	$10.80
Purchase #7	$69.32	12.766%	$78.1694	$78.17	$78.15	$78.20
7 purchase totals =	$942.87		$1,046.1896	$1,046.18	$1,046.15	$1,046.20