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	$75.42	13.461%	$85.5723	$85.57	$85.55	$85.60
Purchase #2	$95.50	9.834%	$104.8915	$104.89	$104.90	$104.90
Purchase #3	$212.83	6.810%	$227.3237	$227.32	$227.30	$227.30
Purchase #4	$41.26	11.218%	$45.8885	$45.89	$45.90	$45.90
Purchase #5	$61.57	13.638%	$69.9669	$69.97	$69.95	$70.00
Purchase #6	$13.69	8.424%	$14.8432	$14.84	$14.85	$14.80
Purchase #7	$219.29	10.489%	$242.2913	$242.29	$242.30	$242.30
7 purchase totals =	$719.56		$790.7774	$790.77	$790.75	$790.80