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	$124.26	8.315%	$134.5922	$134.59	$134.60	$134.60
Purchase #2	$103.35	3.443%	$106.9083	$106.91	$106.90	$106.90
Purchase #3	$79.43	13.782%	$90.377	$90.38	$90.40	$90.40
Purchase #4	$61.29	8.644%	$66.5879	$66.59	$66.60	$66.60
Purchase #5	$219.89	5.342%	$231.6365	$231.64	$231.65	$231.60
Purchase #6	$96.71	3.360%	$99.9595	$99.96	$99.95	$100.00
Purchase #7	$209.98	10.368%	$231.7507	$231.75	$231.75	$231.80
7 purchase totals =	$894.91		$961.8121	$961.82	$961.85	$961.90