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	$34.91	5.106%	$36.6925	$36.69	$36.70	$36.70
Purchase #2	$68.41	5.269%	$72.0145	$72.01	$72.00	$72.00
Purchase #3	$83.82	7.791%	$90.3504	$90.35	$90.35	$90.40
Purchase #4	$230.56	12.674%	$259.7812	$259.78	$259.80	$259.80
Purchase #5	$160.28	5.190%	$168.5985	$168.60	$168.60	$168.60
Purchase #6	$179.66	13.518%	$203.9464	$203.95	$203.95	$203.90
Purchase #7	$77.69	13.707%	$88.339	$88.34	$88.35	$88.30
7 purchase totals =	$835.33		$919.7225	$919.72	$919.75	$919.70