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	$169.48	6.659%	$180.7657	$180.77	$180.75	$180.80
Purchase #2	$32.75	7.640%	$35.2521	$35.25	$35.25	$35.30
Purchase #3	$25.27	7.742%	$27.2264	$27.23	$27.25	$27.20
Purchase #4	$246.55	13.423%	$279.6444	$279.64	$279.65	$279.60
Purchase #5	$138.85	8.703%	$150.9341	$150.93	$150.95	$150.90
Purchase #6	$101.67	9.636%	$111.4669	$111.47	$111.45	$111.50
Purchase #7	$7.64	12.138%	$8.5673	$8.57	$8.55	$8.60
7 purchase totals =	$722.21		$793.8569	$793.86	$793.85	$793.90