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	$34.75	5.271%	$36.5817	$36.58	$36.60	$36.60
Purchase #2	$60.53	11.594%	$67.5478	$67.55	$67.55	$67.50
Purchase #3	$194.83	11.118%	$216.4912	$216.49	$216.50	$216.50
Purchase #4	$18.84	13.142%	$21.316	$21.32	$21.30	$21.30
Purchase #5	$40.42	12.785%	$45.5877	$45.59	$45.60	$45.60
Purchase #6	$178.26	10.438%	$196.8668	$196.87	$196.85	$196.90
Purchase #7	$5.61	5.299%	$5.9073	$5.91	$5.90	$5.90
7 purchase totals =	$533.24		$590.2985	$590.31	$590.30	$590.30