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	$156.30	10.544%	$172.7803	$172.78	$172.80	$172.80
Purchase #2	$128.64	13.197%	$145.6166	$145.62	$145.60	$145.60
Purchase #3	$77.53	4.846%	$81.2871	$81.29	$81.30	$81.30
Purchase #4	$68.73	5.485%	$72.4998	$72.50	$72.50	$72.50
Purchase #5	$182.54	6.851%	$195.0458	$195.05	$195.05	$195.00
Purchase #6	$53.43	12.129%	$59.9105	$59.91	$59.90	$59.90
Purchase #7	$77.56	10.181%	$85.4564	$85.46	$85.45	$85.50
7 purchase totals =	$744.73		$812.5965	$812.61	$812.60	$812.60