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	$235.82	6.264%	$250.5918	$250.59	$250.60	$250.60
Purchase #2	$153.60	12.268%	$172.4436	$172.44	$172.45	$172.40
Purchase #3	$154.79	10.238%	$170.6374	$170.64	$170.65	$170.60
Purchase #4	$60.57	10.462%	$66.9068	$66.91	$66.90	$66.90
Purchase #5	$127.28	6.796%	$135.9299	$135.93	$135.95	$135.90
Purchase #6	$145.88	3.614%	$151.1521	$151.15	$151.15	$151.20
Purchase #7	$35.87	4.600%	$37.52	$37.52	$37.50	$37.50
7 purchase totals =	$913.81		$985.1816	$985.18	$985.20	$985.10