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	$47.59	7.804%	$51.3039	$51.30	$51.30	$51.30
Purchase #2	$33.78	10.570%	$37.3505	$37.35	$37.35	$37.40
Purchase #3	$172.43	13.542%	$195.7805	$195.78	$195.80	$195.80
Purchase #4	$80.34	10.580%	$88.84	$88.84	$88.85	$88.80
Purchase #5	$58.34	10.396%	$64.405	$64.41	$64.40	$64.40
Purchase #6	$37.68	12.806%	$42.5053	$42.51	$42.50	$42.50
Purchase #7	$119.98	11.228%	$133.4514	$133.45	$133.45	$133.50
7 purchase totals =	$550.14		$613.6366	$613.64	$613.65	$613.70