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	$99.31	12.484%	$111.7079	$111.71	$111.70	$111.70
Purchase #2	$178.53	3.211%	$184.2626	$184.26	$184.25	$184.30
Purchase #3	$73.69	12.500%	$82.9013	$82.90	$82.90	$82.90
Purchase #4	$116.54	8.720%	$126.7023	$126.70	$126.70	$126.70
Purchase #5	$222.58	10.838%	$246.7032	$246.70	$246.70	$246.70
Purchase #6	$16.90	10.496%	$18.6738	$18.67	$18.65	$18.70
Purchase #7	$19.81	10.512%	$21.8924	$21.89	$21.90	$21.90
7 purchase totals =	$727.36		$792.8435	$792.83	$792.80	$792.90