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	$135.54	12.484%	$152.4608	$152.46	$152.45	$152.50
Purchase #2	$65.33	4.315%	$68.149	$68.15	$68.15	$68.10
Purchase #3	$235.69	8.124%	$254.8375	$254.84	$254.85	$254.80
Purchase #4	$176.95	6.671%	$188.7543	$188.75	$188.75	$188.80
Purchase #5	$33.60	11.706%	$37.5332	$37.53	$37.55	$37.50
Purchase #6	$56.73	5.403%	$59.7951	$59.80	$59.80	$59.80
Purchase #7	$155.32	6.210%	$164.9654	$164.97	$164.95	$165.00
7 purchase totals =	$859.16		$926.4953	$926.50	$926.50	$926.50