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	$132.96	13.696%	$151.1702	$151.17	$151.15	$151.20
Purchase #2	$108.84	4.334%	$113.5571	$113.56	$113.55	$113.60
Purchase #3	$22.50	10.402%	$24.8405	$24.84	$24.85	$24.80
Purchase #4	$61.25	7.532%	$65.8634	$65.86	$65.85	$65.90
Purchase #5	$106.72	13.501%	$121.1283	$121.13	$121.15	$121.10
Purchase #6	$128.61	6.773%	$137.3208	$137.32	$137.30	$137.30
Purchase #7	$145.46	7.665%	$156.6095	$156.61	$156.60	$156.60
7 purchase totals =	$706.34		$770.4898	$770.49	$770.45	$770.50