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	$63.92	13.407%	$72.4898	$72.49	$72.50	$72.50
Purchase #2	$64.32	11.473%	$71.6994	$71.70	$71.70	$71.70
Purchase #3	$108.64	13.817%	$123.6508	$123.65	$123.65	$123.70
Purchase #4	$33.73	5.583%	$35.6131	$35.61	$35.60	$35.60
Purchase #5	$85.31	3.776%	$88.5313	$88.53	$88.55	$88.50
Purchase #6	$168.82	8.398%	$182.9975	$183.00	$183.00	$183.00
Purchase #7	$208.72	13.633%	$237.1748	$237.17	$237.15	$237.20
7 purchase totals =	$733.46		$812.1567	$812.15	$812.15	$812.20