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	$65.71	10.398%	$72.5425	$72.54	$72.55	$72.50
Purchase #2	$137.38	13.557%	$156.0046	$156.00	$156.00	$156.00
Purchase #3	$87.77	7.429%	$94.2904	$94.29	$94.30	$94.30
Purchase #4	$132.45	8.669%	$143.9321	$143.93	$143.95	$143.90
Purchase #5	$99.78	13.684%	$113.4339	$113.43	$113.45	$113.40
Purchase #6	$160.51	12.460%	$180.5095	$180.51	$180.50	$180.50
Purchase #7	$144.96	8.632%	$157.4729	$157.47	$157.45	$157.50
7 purchase totals =	$828.56		$918.1859	$918.17	$918.20	$918.10