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	$153.35	12.473%	$172.4773	$172.48	$172.50	$172.50
Purchase #2	$132.98	8.648%	$144.4801	$144.48	$144.50	$144.50
Purchase #3	$106.75	11.495%	$119.0209	$119.02	$119.00	$119.00
Purchase #4	$6.56	10.191%	$7.2285	$7.23	$7.25	$7.20
Purchase #5	$9.55	12.352%	$10.7296	$10.73	$10.75	$10.70
Purchase #6	$198.59	4.543%	$207.6119	$207.61	$207.60	$207.60
Purchase #7	$218.29	11.277%	$242.9066	$242.91	$242.90	$242.90
7 purchase totals =	$826.07		$904.4549	$904.46	$904.50	$904.40