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	$154.92	10.383%	$171.0053	$171.01	$171.00	$171.00
Purchase #2	$75.26	7.485%	$80.8932	$80.89	$80.90	$80.90
Purchase #3	$85.73	5.577%	$90.5112	$90.51	$90.50	$90.50
Purchase #4	$135.43	7.749%	$145.9245	$145.92	$145.90	$145.90
Purchase #5	$74.87	10.503%	$82.7336	$82.73	$82.75	$82.70
Purchase #6	$46.74	8.301%	$50.6199	$50.62	$50.60	$50.60
Purchase #7	$24.87	6.552%	$26.4995	$26.50	$26.50	$26.50
7 purchase totals =	$597.82		$648.1872	$648.18	$648.15	$648.10