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	$157.68	13.468%	$178.9163	$178.92	$178.90	$178.90
Purchase #2	$49.54	12.226%	$55.5968	$55.60	$55.60	$55.60
Purchase #3	$143.28	11.412%	$159.6311	$159.63	$159.65	$159.60
Purchase #4	$146.57	8.787%	$159.4491	$159.45	$159.45	$159.40
Purchase #5	$185.52	7.539%	$199.5064	$199.51	$199.50	$199.50
Purchase #6	$245.88	4.514%	$256.979	$256.98	$257.00	$257.00
Purchase #7	$161.69	6.867%	$172.7933	$172.79	$172.80	$172.80
7 purchase totals =	$1,090.16		$1,182.8720	$1,182.88	$1,182.90	$1,182.80