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	$233.54	5.304%	$245.927	$245.93	$245.95	$245.90
Purchase #2	$77.56	11.648%	$86.5942	$86.59	$86.60	$86.60
Purchase #3	$157.59	10.136%	$173.5633	$173.56	$173.55	$173.60
Purchase #4	$141.71	6.641%	$151.121	$151.12	$151.10	$151.10
Purchase #5	$152.48	13.176%	$172.5708	$172.57	$172.55	$172.60
Purchase #6	$12.51	11.306%	$13.9244	$13.92	$13.90	$13.90
Purchase #7	$33.73	7.310%	$36.1957	$36.20	$36.20	$36.20
7 purchase totals =	$809.12		$879.8964	$879.89	$879.85	$879.90