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	$36.52	7.571%	$39.2849	$39.28	$39.30	$39.30
Purchase #2	$134.75	11.142%	$149.7638	$149.76	$149.75	$149.80
Purchase #3	$95.68	13.805%	$108.8886	$108.89	$108.90	$108.90
Purchase #4	$42.53	3.174%	$43.8799	$43.88	$43.90	$43.90
Purchase #5	$29.90	10.286%	$32.9755	$32.98	$33.00	$33.00
Purchase #6	$136.96	10.353%	$151.1395	$151.14	$151.15	$151.10
Purchase #7	$28.37	6.775%	$30.2921	$30.29	$30.30	$30.30
7 purchase totals =	$504.71		$556.2243	$556.22	$556.30	$556.30