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	$62.83	13.584%	$71.3648	$71.36	$71.35	$71.40
Purchase #2	$30.81	6.814%	$32.9094	$32.91	$32.90	$32.90
Purchase #3	$35.92	4.738%	$37.6219	$37.62	$37.60	$37.60
Purchase #4	$17.40	7.485%	$18.7024	$18.70	$18.70	$18.70
Purchase #5	$46.82	8.290%	$50.7014	$50.70	$50.70	$50.70
Purchase #6	$177.96	12.451%	$200.1178	$200.12	$200.10	$200.10
Purchase #7	$177.90	5.164%	$187.0868	$187.09	$187.10	$187.10
7 purchase totals =	$549.64		$598.5045	$598.50	$598.45	$598.50