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	$114.89	8.536%	$124.697	$124.70	$124.70	$124.70
Purchase #2	$88.36	13.248%	$100.0659	$100.07	$100.05	$100.10
Purchase #3	$131.84	4.579%	$137.877	$137.88	$137.90	$137.90
Purchase #4	$67.65	4.782%	$70.885	$70.89	$70.90	$70.90
Purchase #5	$245.25	5.129%	$257.8289	$257.83	$257.85	$257.80
Purchase #6	$42.82	5.484%	$45.1682	$45.17	$45.15	$45.20
Purchase #7	$141.85	13.448%	$160.926	$160.93	$160.95	$160.90
7 purchase totals =	$832.66		$897.4480	$897.47	$897.50	$897.50