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	$150.77	12.711%	$169.9344	$169.93	$169.95	$169.90
Purchase #2	$77.85	8.827%	$84.7218	$84.72	$84.70	$84.70
Purchase #3	$29.52	10.446%	$32.6037	$32.60	$32.60	$32.60
Purchase #4	$65.69	6.796%	$70.1543	$70.15	$70.15	$70.20
Purchase #5	$40.56	4.315%	$42.3102	$42.31	$42.30	$42.30
Purchase #6	$155.70	8.353%	$168.7056	$168.71	$168.70	$168.70
Purchase #7	$231.83	11.675%	$258.8962	$258.90	$258.90	$258.90
7 purchase totals =	$751.92		$827.3262	$827.32	$827.30	$827.30