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	$27.35	13.418%	$31.0198	$31.02	$31.00	$31.00
Purchase #2	$204.31	6.306%	$217.1938	$217.19	$217.20	$217.20
Purchase #3	$64.32	4.776%	$67.3919	$67.39	$67.40	$67.40
Purchase #4	$9.67	9.789%	$10.6166	$10.62	$10.60	$10.60
Purchase #5	$164.57	4.650%	$172.2225	$172.22	$172.20	$172.20
Purchase #6	$240.36	12.840%	$271.2222	$271.22	$271.20	$271.20
Purchase #7	$11.74	3.610%	$12.1638	$12.16	$12.15	$12.20
7 purchase totals =	$722.32		$781.8306	$781.82	$781.75	$781.80