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	$86.51	3.222%	$89.2974	$89.30	$89.30	$89.30
Purchase #2	$81.39	10.155%	$89.6552	$89.66	$89.65	$89.70
Purchase #3	$46.84	8.674%	$50.9029	$50.90	$50.90	$50.90
Purchase #4	$15.59	12.298%	$17.5073	$17.51	$17.50	$17.50
Purchase #5	$213.69	10.843%	$236.8604	$236.86	$236.85	$236.90
Purchase #6	$105.49	10.283%	$116.3375	$116.34	$116.35	$116.30
Purchase #7	$228.67	13.613%	$259.7988	$259.80	$259.80	$259.80
7 purchase totals =	$778.18		$860.3595	$860.37	$860.35	$860.40