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	$127.89	7.278%	$137.1978	$137.20	$137.20	$137.20
Purchase #2	$54.59	8.607%	$59.2886	$59.29	$59.30	$59.30
Purchase #3	$212.47	7.131%	$227.6212	$227.62	$227.60	$227.60
Purchase #4	$70.98	4.722%	$74.3317	$74.33	$74.35	$74.30
Purchase #5	$71.82	11.127%	$79.8114	$79.81	$79.80	$79.80
Purchase #6	$95.88	11.170%	$106.5898	$106.59	$106.60	$106.60
Purchase #7	$119.57	10.798%	$132.4812	$132.48	$132.50	$132.50
7 purchase totals =	$753.20		$817.3217	$817.32	$817.35	$817.30