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	$109.35	13.135%	$123.7131	$123.71	$123.70	$123.70
Purchase #2	$234.68	12.730%	$264.5548	$264.55	$264.55	$264.60
Purchase #3	$55.96	5.791%	$59.2006	$59.20	$59.20	$59.20
Purchase #4	$196.63	11.304%	$218.8571	$218.86	$218.85	$218.90
Purchase #5	$29.47	7.604%	$31.7109	$31.71	$31.70	$31.70
Purchase #6	$37.62	10.616%	$41.6137	$41.61	$41.60	$41.60
Purchase #7	$16.54	9.819%	$18.1641	$18.16	$18.15	$18.20
7 purchase totals =	$680.25		$757.8143	$757.80	$757.75	$757.90