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	$61.99	8.862%	$67.4836	$67.48	$67.50	$67.50
Purchase #2	$150.93	11.592%	$168.4258	$168.43	$168.45	$168.40
Purchase #3	$126.74	3.712%	$131.4446	$131.44	$131.45	$131.40
Purchase #4	$153.48	7.561%	$165.0846	$165.08	$165.10	$165.10
Purchase #5	$41.28	3.841%	$42.8656	$42.87	$42.85	$42.90
Purchase #6	$54.53	4.442%	$56.9522	$56.95	$56.95	$57.00
Purchase #7	$14.29	6.634%	$15.238	$15.24	$15.25	$15.20
7 purchase totals =	$603.24		$647.4944	$647.49	$647.55	$647.50