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	$230.96	10.240%	$254.6103	$254.61	$254.60	$254.60
Purchase #2	$212.73	11.657%	$237.5279	$237.53	$237.55	$237.50
Purchase #3	$40.56	7.175%	$43.4702	$43.47	$43.45	$43.50
Purchase #4	$156.95	8.210%	$169.8356	$169.84	$169.85	$169.80
Purchase #5	$28.83	8.554%	$31.2961	$31.30	$31.30	$31.30
Purchase #6	$133.83	4.557%	$139.9286	$139.93	$139.95	$139.90
Purchase #7	$32.38	8.394%	$35.098	$35.10	$35.10	$35.10
7 purchase totals =	$836.24		$911.7667	$911.78	$911.80	$911.70