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	$29.29	12.401%	$32.9223	$32.92	$32.90	$32.90
Purchase #2	$15.85	4.402%	$16.5477	$16.55	$16.55	$16.50
Purchase #3	$30.53	10.548%	$33.7503	$33.75	$33.75	$33.80
Purchase #4	$234.88	12.492%	$264.2212	$264.22	$264.20	$264.20
Purchase #5	$29.46	6.735%	$31.4441	$31.44	$31.45	$31.40
Purchase #6	$45.81	9.505%	$50.1642	$50.16	$50.15	$50.20
Purchase #7	$130.57	8.393%	$141.5287	$141.53	$141.55	$141.50
7 purchase totals =	$516.39		$570.5785	$570.57	$570.55	$570.50