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	$94.35	9.473%	$103.2878	$103.29	$103.30	$103.30
Purchase #2	$32.45	10.710%	$35.9254	$35.93	$35.95	$35.90
Purchase #3	$148.72	10.796%	$164.7758	$164.78	$164.80	$164.80
Purchase #4	$164.94	3.804%	$171.2143	$171.21	$171.20	$171.20
Purchase #5	$6.26	3.273%	$6.4649	$6.46	$6.45	$6.50
Purchase #6	$41.35	10.576%	$45.7232	$45.72	$45.70	$45.70
Purchase #7	$215.55	13.398%	$244.4294	$244.43	$244.45	$244.40
7 purchase totals =	$703.62		$771.8208	$771.82	$771.85	$771.80