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	$81.85	6.781%	$87.4002	$87.40	$87.40	$87.40
Purchase #2	$44.50	13.626%	$50.5636	$50.56	$50.55	$50.60
Purchase #3	$81.34	9.799%	$89.3105	$89.31	$89.30	$89.30
Purchase #4	$187.29	8.679%	$203.5449	$203.54	$203.55	$203.50
Purchase #5	$220.95	11.519%	$246.4012	$246.40	$246.40	$246.40
Purchase #6	$78.73	10.205%	$86.7644	$86.76	$86.75	$86.80
Purchase #7	$162.27	10.865%	$179.9006	$179.90	$179.90	$179.90
7 purchase totals =	$856.93		$943.8854	$943.87	$943.85	$943.90