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	$37.62	12.626%	$42.3699	$42.37	$42.35	$42.40
Purchase #2	$111.52	5.161%	$117.2755	$117.28	$117.30	$117.30
Purchase #3	$33.80	8.526%	$36.6818	$36.68	$36.70	$36.70
Purchase #4	$203.60	12.283%	$228.6082	$228.61	$228.60	$228.60
Purchase #5	$156.66	7.823%	$168.9155	$168.92	$168.90	$168.90
Purchase #6	$6.87	10.851%	$7.6155	$7.62	$7.60	$7.60
Purchase #7	$43.52	8.691%	$47.3023	$47.30	$47.30	$47.30
7 purchase totals =	$593.59		$648.7687	$648.78	$648.75	$648.80