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	$38.30	12.557%	$43.1093	$43.11	$43.10	$43.10
Purchase #2	$47.92	6.145%	$50.8647	$50.86	$50.85	$50.90
Purchase #3	$94.46	8.223%	$102.2274	$102.23	$102.25	$102.20
Purchase #4	$250.35	12.450%	$281.5186	$281.52	$281.50	$281.50
Purchase #5	$31.25	9.137%	$34.1053	$34.11	$34.10	$34.10
Purchase #6	$146.28	3.388%	$151.236	$151.24	$151.25	$151.20
Purchase #7	$35.85	12.344%	$40.2753	$40.28	$40.30	$40.30
7 purchase totals =	$644.41		$703.3366	$703.35	$703.35	$703.30