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	$136.83	11.678%	$152.809	$152.81	$152.80	$152.80
Purchase #2	$236.90	8.399%	$256.7972	$256.80	$256.80	$256.80
Purchase #3	$148.70	10.645%	$164.5291	$164.53	$164.55	$164.50
Purchase #4	$241.70	6.545%	$257.5193	$257.52	$257.50	$257.50
Purchase #5	$125.34	4.406%	$130.8625	$130.86	$130.85	$130.90
Purchase #6	$53.56	13.502%	$60.7917	$60.79	$60.80	$60.80
Purchase #7	$126.64	3.682%	$131.3029	$131.30	$131.30	$131.30
7 purchase totals =	$1,069.67		$1,154.6117	$1,154.61	$1,154.60	$1,154.60