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	$85.82	3.382%	$88.7224	$88.72	$88.70	$88.70
Purchase #2	$107.79	3.549%	$111.6155	$111.62	$111.60	$111.60
Purchase #3	$71.77	3.126%	$74.0135	$74.01	$74.00	$74.00
Purchase #4	$90.78	8.566%	$98.5562	$98.56	$98.55	$98.60
Purchase #5	$164.78	3.445%	$170.4567	$170.46	$170.45	$170.50
Purchase #6	$34.29	10.450%	$37.8733	$37.87	$37.85	$37.90
Purchase #7	$87.52	7.851%	$94.3912	$94.39	$94.40	$94.40
7 purchase totals =	$642.75		$675.6288	$675.63	$675.55	$675.70