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	$110.46	9.164%	$120.5826	$120.58	$120.60	$120.60
Purchase #2	$176.38	13.731%	$200.5987	$200.60	$200.60	$200.60
Purchase #3	$35.97	3.389%	$37.189	$37.19	$37.20	$37.20
Purchase #4	$28.67	6.630%	$30.5708	$30.57	$30.55	$30.60
Purchase #5	$156.49	3.749%	$162.3568	$162.36	$162.35	$162.40
Purchase #6	$85.31	5.670%	$90.1471	$90.15	$90.15	$90.10
Purchase #7	$34.91	8.266%	$37.7957	$37.80	$37.80	$37.80
7 purchase totals =	$628.19		$679.2407	$679.25	$679.25	$679.30