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	$59.26	8.228%	$64.1359	$64.14	$64.15	$64.10
Purchase #2	$220.96	13.299%	$250.3455	$250.35	$250.35	$250.30
Purchase #3	$13.90	13.443%	$15.7686	$15.77	$15.75	$15.80
Purchase #4	$85.28	8.853%	$92.8298	$92.83	$92.85	$92.80
Purchase #5	$156.44	10.504%	$172.8725	$172.87	$172.85	$172.90
Purchase #6	$42.74	12.650%	$48.1466	$48.15	$48.15	$48.10
Purchase #7	$156.88	4.190%	$163.4533	$163.45	$163.45	$163.50
7 purchase totals =	$735.46		$807.5522	$807.56	$807.55	$807.50