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	$33.25	5.751%	$35.1622	$35.16	$35.15	$35.20
Purchase #2	$239.65	6.609%	$255.4885	$255.49	$255.50	$255.50
Purchase #3	$114.52	7.787%	$123.4377	$123.44	$123.45	$123.40
Purchase #4	$205.69	6.674%	$219.4178	$219.42	$219.40	$219.40
Purchase #5	$59.88	13.191%	$67.7788	$67.78	$67.80	$67.80
Purchase #6	$46.36	4.764%	$48.5686	$48.57	$48.55	$48.60
Purchase #7	$65.53	10.404%	$72.3477	$72.35	$72.35	$72.30
7 purchase totals =	$764.88		$822.2013	$822.21	$822.20	$822.20