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	$29.76	12.431%	$33.4595	$33.46	$33.45	$33.50
Purchase #2	$201.44	5.651%	$212.8234	$212.82	$212.80	$212.80
Purchase #3	$65.52	11.324%	$72.9395	$72.94	$72.95	$72.90
Purchase #4	$33.79	4.773%	$35.4028	$35.40	$35.40	$35.40
Purchase #5	$250.97	3.778%	$260.4516	$260.45	$260.45	$260.50
Purchase #6	$31.52	4.113%	$32.8164	$32.82	$32.80	$32.80
Purchase #7	$33.49	11.487%	$37.337	$37.34	$37.35	$37.30
7 purchase totals =	$646.49		$685.2302	$685.23	$685.20	$685.20