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	$54.75	7.322%	$58.7588	$58.76	$58.75	$58.80
Purchase #2	$136.59	10.770%	$151.3007	$151.30	$151.30	$151.30
Purchase #3	$34.92	13.166%	$39.5176	$39.52	$39.50	$39.50
Purchase #4	$116.57	6.778%	$124.4711	$124.47	$124.45	$124.50
Purchase #5	$196.36	13.302%	$222.4798	$222.48	$222.50	$222.50
Purchase #6	$95.76	11.635%	$106.9017	$106.90	$106.90	$106.90
Purchase #7	$36.38	9.157%	$39.7113	$39.71	$39.70	$39.70
7 purchase totals =	$671.33		$743.1410	$743.14	$743.10	$743.20