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	$132.89	4.282%	$138.5803	$138.58	$138.60	$138.60
Purchase #2	$153.59	7.646%	$165.3335	$165.33	$165.35	$165.30
Purchase #3	$62.54	5.818%	$66.1786	$66.18	$66.20	$66.20
Purchase #4	$209.95	10.283%	$231.5392	$231.54	$231.55	$231.50
Purchase #5	$205.55	6.332%	$218.5654	$218.57	$218.55	$218.60
Purchase #6	$76.30	7.660%	$82.1446	$82.14	$82.15	$82.10
Purchase #7	$152.59	6.738%	$162.8715	$162.87	$162.85	$162.90
7 purchase totals =	$993.41		$1,065.2131	$1,065.21	$1,065.25	$1,065.20