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	$134.28	4.648%	$140.5213	$140.52	$140.50	$140.50
Purchase #2	$75.38	10.184%	$83.0567	$83.06	$83.05	$83.10
Purchase #3	$136.57	3.110%	$140.8173	$140.82	$140.80	$140.80
Purchase #4	$21.42	12.855%	$24.1735	$24.17	$24.15	$24.20
Purchase #5	$32.47	13.437%	$36.833	$36.83	$36.85	$36.80
Purchase #6	$28.62	13.108%	$32.3715	$32.37	$32.35	$32.40
Purchase #7	$41.98	11.594%	$46.8472	$46.85	$46.85	$46.80
7 purchase totals =	$470.72		$504.6205	$504.62	$504.55	$504.60