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	$59.89	12.788%	$67.5487	$67.55	$67.55	$67.50
Purchase #2	$121.97	8.280%	$132.0691	$132.07	$132.05	$132.10
Purchase #3	$10.78	12.367%	$12.1132	$12.11	$12.10	$12.10
Purchase #4	$105.57	11.180%	$117.3727	$117.37	$117.35	$117.40
Purchase #5	$216.52	10.474%	$239.1983	$239.20	$239.20	$239.20
Purchase #6	$117.33	5.258%	$123.4992	$123.50	$123.50	$123.50
Purchase #7	$171.83	4.406%	$179.4008	$179.40	$179.40	$179.40
7 purchase totals =	$803.89		$871.2020	$871.20	$871.15	$871.20