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	$138.80	13.533%	$157.5838	$157.58	$157.60	$157.60
Purchase #2	$97.52	12.504%	$109.7139	$109.71	$109.70	$109.70
Purchase #3	$250.34	4.188%	$260.8242	$260.82	$260.80	$260.80
Purchase #4	$117.60	5.639%	$124.2315	$124.23	$124.25	$124.20
Purchase #5	$58.45	11.700%	$65.2887	$65.29	$65.30	$65.30
Purchase #6	$228.48	5.874%	$241.9009	$241.90	$241.90	$241.90
Purchase #7	$165.94	3.596%	$171.9072	$171.91	$171.90	$171.90
7 purchase totals =	$1,057.13		$1,131.4502	$1,131.44	$1,131.45	$1,131.40