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	$37.80	11.336%	$42.085	$42.09	$42.10	$42.10
Purchase #2	$105.33	8.610%	$114.3989	$114.40	$114.40	$114.40
Purchase #3	$160.93	3.798%	$167.0421	$167.04	$167.05	$167.00
Purchase #4	$129.73	7.223%	$139.1004	$139.10	$139.10	$139.10
Purchase #5	$236.89	4.417%	$247.3534	$247.35	$247.35	$247.40
Purchase #6	$123.45	12.188%	$138.4961	$138.50	$138.50	$138.50
Purchase #7	$34.49	8.865%	$37.5475	$37.55	$37.55	$37.50
7 purchase totals =	$828.62		$886.0234	$886.03	$886.05	$886.00