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	$208.71	6.690%	$222.6727	$222.67	$222.65	$222.70
Purchase #2	$189.96	13.803%	$216.1802	$216.18	$216.20	$216.20
Purchase #3	$53.49	10.602%	$59.161	$59.16	$59.15	$59.20
Purchase #4	$98.78	11.751%	$110.3876	$110.39	$110.40	$110.40
Purchase #5	$153.63	7.375%	$164.9602	$164.96	$164.95	$165.00
Purchase #6	$18.72	7.605%	$20.1437	$20.14	$20.15	$20.10
Purchase #7	$82.49	5.407%	$86.9502	$86.95	$86.95	$87.00
7 purchase totals =	$805.78		$880.4556	$880.45	$880.45	$880.60