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	$56.89	8.311%	$61.6181	$61.62	$61.60	$61.60
Purchase #2	$84.32	6.870%	$90.1128	$90.11	$90.10	$90.10
Purchase #3	$126.53	10.851%	$140.2598	$140.26	$140.25	$140.30
Purchase #4	$66.63	13.379%	$75.5444	$75.54	$75.55	$75.50
Purchase #5	$47.63	4.482%	$49.7648	$49.76	$49.75	$49.80
Purchase #6	$88.94	11.693%	$99.3398	$99.34	$99.35	$99.30
Purchase #7	$99.46	3.676%	$103.1161	$103.12	$103.10	$103.10
7 purchase totals =	$570.40		$619.7558	$619.75	$619.70	$619.70