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	$32.59	3.772%	$33.8193	$33.82	$33.80	$33.80
Purchase #2	$33.54	4.623%	$35.0906	$35.09	$35.10	$35.10
Purchase #3	$29.73	10.376%	$32.8148	$32.81	$32.80	$32.80
Purchase #4	$50.93	4.563%	$53.2539	$53.25	$53.25	$53.30
Purchase #5	$236.32	12.233%	$265.229	$265.23	$265.25	$265.20
Purchase #6	$156.50	9.733%	$171.7321	$171.73	$171.75	$171.70
Purchase #7	$13.31	8.342%	$14.4203	$14.42	$14.40	$14.40
7 purchase totals =	$552.92		$606.3600	$606.35	$606.35	$606.30