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	$35.67	11.753%	$39.8623	$39.86	$39.85	$39.90
Purchase #2	$93.58	7.515%	$100.6125	$100.61	$100.60	$100.60
Purchase #3	$212.72	10.667%	$235.4108	$235.41	$235.40	$235.40
Purchase #4	$205.49	3.139%	$211.9403	$211.94	$211.95	$211.90
Purchase #5	$37.34	12.705%	$42.084	$42.08	$42.10	$42.10
Purchase #6	$146.44	9.416%	$160.2288	$160.23	$160.25	$160.20
Purchase #7	$111.57	12.466%	$125.4783	$125.48	$125.50	$125.50
7 purchase totals =	$842.81		$915.6170	$915.61	$915.65	$915.60