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	$32.79	11.503%	$36.5618	$36.56	$36.55	$36.60
Purchase #2	$115.74	10.708%	$128.1334	$128.13	$128.15	$128.10
Purchase #3	$72.87	8.259%	$78.8883	$78.89	$78.90	$78.90
Purchase #4	$28.85	5.272%	$30.371	$30.37	$30.35	$30.40
Purchase #5	$38.56	10.547%	$42.6269	$42.63	$42.65	$42.60
Purchase #6	$33.65	10.250%	$37.0991	$37.10	$37.10	$37.10
Purchase #7	$247.81	6.154%	$263.0602	$263.06	$263.05	$263.10
7 purchase totals =	$570.27		$616.7407	$616.74	$616.75	$616.80