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	$154.88	8.693%	$168.3437	$168.34	$168.35	$168.30
Purchase #2	$99.87	9.542%	$109.3996	$109.40	$109.40	$109.40
Purchase #3	$111.69	5.534%	$117.8709	$117.87	$117.85	$117.90
Purchase #4	$209.35	6.533%	$223.0268	$223.03	$223.05	$223.00
Purchase #5	$207.95	9.551%	$227.8113	$227.81	$227.80	$227.80
Purchase #6	$59.71	13.434%	$67.7314	$67.73	$67.75	$67.70
Purchase #7	$34.38	7.616%	$36.9984	$37.00	$37.00	$37.00
7 purchase totals =	$877.83		$951.1821	$951.18	$951.20	$951.10