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	$50.29	4.451%	$52.5284	$52.53	$52.55	$52.50
Purchase #2	$158.85	4.603%	$166.1619	$166.16	$166.15	$166.20
Purchase #3	$162.87	3.402%	$168.4108	$168.41	$168.40	$168.40
Purchase #4	$148.50	11.248%	$165.2033	$165.20	$165.20	$165.20
Purchase #5	$35.95	9.842%	$39.4882	$39.49	$39.50	$39.50
Purchase #6	$126.93	5.717%	$134.1866	$134.19	$134.20	$134.20
Purchase #7	$33.59	12.800%	$37.8895	$37.89	$37.90	$37.90
7 purchase totals =	$716.98		$763.8687	$763.87	$763.90	$763.90