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	$134.82	8.652%	$146.4846	$146.48	$146.50	$146.50
Purchase #2	$80.46	4.159%	$83.8063	$83.81	$83.80	$83.80
Purchase #3	$30.51	12.539%	$34.3356	$34.34	$34.35	$34.30
Purchase #4	$135.35	4.222%	$141.0645	$141.06	$141.05	$141.10
Purchase #5	$183.95	4.300%	$191.8599	$191.86	$191.85	$191.90
Purchase #6	$145.93	7.298%	$156.58	$156.58	$156.60	$156.60
Purchase #7	$41.95	11.451%	$46.7537	$46.75	$46.75	$46.80
7 purchase totals =	$752.97		$800.8846	$800.88	$800.90	$801.00