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	$30.63	9.810%	$33.6348	$33.63	$33.65	$33.60
Purchase #2	$77.73	3.616%	$80.5407	$80.54	$80.55	$80.50
Purchase #3	$44.90	7.443%	$48.2419	$48.24	$48.25	$48.20
Purchase #4	$90.53	11.483%	$100.9256	$100.93	$100.95	$100.90
Purchase #5	$136.34	4.255%	$142.1413	$142.14	$142.15	$142.10
Purchase #6	$68.36	11.693%	$76.3533	$76.35	$76.35	$76.40
Purchase #7	$12.68	7.472%	$13.6274	$13.63	$13.65	$13.60
7 purchase totals =	$461.17		$495.4650	$495.46	$495.55	$495.30