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	$31.25	13.215%	$35.3797	$35.38	$35.40	$35.40
Purchase #2	$213.63	9.643%	$234.2303	$234.23	$234.25	$234.20
Purchase #3	$210.70	6.120%	$223.5948	$223.59	$223.60	$223.60
Purchase #4	$128.67	13.105%	$145.5322	$145.53	$145.55	$145.50
Purchase #5	$206.54	7.103%	$221.2105	$221.21	$221.20	$221.20
Purchase #6	$219.42	8.686%	$238.4788	$238.48	$238.50	$238.50
Purchase #7	$50.43	9.136%	$55.0373	$55.04	$55.05	$55.00
7 purchase totals =	$1,060.64		$1,153.4636	$1,153.46	$1,153.55	$1,153.40