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	$54.67	4.524%	$57.1433	$57.14	$57.15	$57.10
Purchase #2	$163.77	11.768%	$183.0425	$183.04	$183.05	$183.00
Purchase #3	$127.42	12.402%	$143.2226	$143.22	$143.20	$143.20
Purchase #4	$35.68	7.116%	$38.219	$38.22	$38.20	$38.20
Purchase #5	$24.89	6.814%	$26.586	$26.59	$26.60	$26.60
Purchase #6	$248.86	8.342%	$269.6199	$269.62	$269.60	$269.60
Purchase #7	$109.72	6.185%	$116.5062	$116.51	$116.50	$116.50
7 purchase totals =	$765.01		$834.3395	$834.34	$834.30	$834.20