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	$108.40	3.436%	$112.1246	$112.12	$112.10	$112.10
Purchase #2	$141.26	10.690%	$156.3607	$156.36	$156.35	$156.40
Purchase #3	$146.77	9.538%	$160.7689	$160.77	$160.75	$160.80
Purchase #4	$5.29	12.243%	$5.9377	$5.94	$5.95	$5.90
Purchase #5	$94.68	7.161%	$101.46	$101.46	$101.45	$101.50
Purchase #6	$168.61	4.267%	$175.8046	$175.80	$175.80	$175.80
Purchase #7	$173.82	13.240%	$196.8338	$196.83	$196.85	$196.80
7 purchase totals =	$838.83		$909.2903	$909.28	$909.25	$909.30