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	$123.70	9.352%	$135.2684	$135.27	$135.25	$135.30
Purchase #2	$43.61	5.164%	$45.862	$45.86	$45.85	$45.90
Purchase #3	$39.97	11.337%	$44.5014	$44.50	$44.50	$44.50
Purchase #4	$180.51	5.340%	$190.1492	$190.15	$190.15	$190.10
Purchase #5	$48.53	8.153%	$52.4867	$52.49	$52.50	$52.50
Purchase #6	$211.30	4.559%	$220.9332	$220.93	$220.95	$220.90
Purchase #7	$140.40	7.159%	$150.4512	$150.45	$150.45	$150.50
7 purchase totals =	$788.02		$839.6521	$839.65	$839.65	$839.70