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	$130.85	5.297%	$137.7811	$137.78	$137.80	$137.80
Purchase #2	$78.78	5.180%	$82.8608	$82.86	$82.85	$82.90
Purchase #3	$21.31	6.135%	$22.6174	$22.62	$22.60	$22.60
Purchase #4	$239.92	6.263%	$254.9462	$254.95	$254.95	$254.90
Purchase #5	$41.60	12.484%	$46.7933	$46.79	$46.80	$46.80
Purchase #6	$128.40	12.826%	$144.8686	$144.87	$144.85	$144.90
Purchase #7	$122.64	11.434%	$136.6627	$136.66	$136.65	$136.70
7 purchase totals =	$763.50		$826.5301	$826.53	$826.50	$826.60