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	$57.64	3.205%	$59.4874	$59.49	$59.50	$59.50
Purchase #2	$108.72	3.857%	$112.9133	$112.91	$112.90	$112.90
Purchase #3	$234.46	12.692%	$264.2177	$264.22	$264.20	$264.20
Purchase #4	$72.63	11.746%	$81.1611	$81.16	$81.15	$81.20
Purchase #5	$176.91	8.204%	$191.4237	$191.42	$191.40	$191.40
Purchase #6	$175.99	11.700%	$196.5808	$196.58	$196.60	$196.60
Purchase #7	$231.64	12.569%	$260.7548	$260.75	$260.75	$260.80
7 purchase totals =	$1,057.99		$1,166.5388	$1,166.53	$1,166.50	$1,166.60