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	$90.82	9.404%	$99.3607	$99.36	$99.35	$99.40
Purchase #2	$81.60	11.665%	$91.1186	$91.12	$91.10	$91.10
Purchase #3	$102.66	12.459%	$115.4504	$115.45	$115.45	$115.50
Purchase #4	$217.84	13.619%	$247.5076	$247.51	$247.50	$247.50
Purchase #5	$32.67	7.246%	$35.0373	$35.04	$35.05	$35.00
Purchase #6	$238.43	6.333%	$253.5298	$253.53	$253.55	$253.50
Purchase #7	$90.52	8.808%	$98.493	$98.49	$98.50	$98.50
7 purchase totals =	$854.54		$940.4974	$940.50	$940.50	$940.50