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	$28.28	10.265%	$31.1829	$31.18	$31.20	$31.20
Purchase #2	$69.82	11.833%	$78.0818	$78.08	$78.10	$78.10
Purchase #3	$30.89	11.198%	$34.3491	$34.35	$34.35	$34.30
Purchase #4	$157.69	6.755%	$168.342	$168.34	$168.35	$168.30
Purchase #5	$176.83	11.479%	$197.1283	$197.13	$197.15	$197.10
Purchase #6	$42.40	13.393%	$48.0786	$48.08	$48.10	$48.10
Purchase #7	$9.41	11.712%	$10.5121	$10.51	$10.50	$10.50
7 purchase totals =	$515.32		$567.6748	$567.67	$567.75	$567.60