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	$42.49	11.588%	$47.4137	$47.41	$47.40	$47.40
Purchase #2	$10.35	5.192%	$10.8874	$10.89	$10.90	$10.90
Purchase #3	$61.47	6.685%	$65.5793	$65.58	$65.60	$65.60
Purchase #4	$90.51	11.683%	$101.0843	$101.08	$101.10	$101.10
Purchase #5	$45.81	10.868%	$50.7886	$50.79	$50.80	$50.80
Purchase #6	$214.78	13.310%	$243.3672	$243.37	$243.35	$243.40
Purchase #7	$134.74	13.447%	$152.8585	$152.86	$152.85	$152.90
7 purchase totals =	$600.15		$671.9790	$671.98	$672.00	$672.10