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	$140.62	10.809%	$155.8196	$155.82	$155.80	$155.80
Purchase #2	$57.66	6.802%	$61.582	$61.58	$61.60	$61.60
Purchase #3	$14.63	8.259%	$15.8383	$15.84	$15.85	$15.80
Purchase #4	$71.46	5.432%	$75.3417	$75.34	$75.35	$75.30
Purchase #5	$60.39	7.162%	$64.7151	$64.72	$64.70	$64.70
Purchase #6	$238.83	6.865%	$255.2257	$255.23	$255.25	$255.20
Purchase #7	$33.67	13.823%	$38.3242	$38.32	$38.30	$38.30
7 purchase totals =	$617.26		$666.8466	$666.85	$666.85	$666.70