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	$49.42	4.245%	$51.5179	$51.52	$51.50	$51.50
Purchase #2	$72.84	4.638%	$76.2183	$76.22	$76.20	$76.20
Purchase #3	$52.91	11.594%	$59.0444	$59.04	$59.05	$59.00
Purchase #4	$22.37	5.251%	$23.5446	$23.54	$23.55	$23.50
Purchase #5	$137.53	12.626%	$154.8945	$154.89	$154.90	$154.90
Purchase #6	$49.82	10.432%	$55.0172	$55.02	$55.00	$55.00
Purchase #7	$85.67	5.131%	$90.0657	$90.07	$90.05	$90.10
7 purchase totals =	$470.56		$510.3026	$510.30	$510.25	$510.20