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	$64.71	12.508%	$72.8039	$72.80	$72.80	$72.80
Purchase #2	$6.27	3.464%	$6.4872	$6.49	$6.50	$6.50
Purchase #3	$128.84	9.736%	$141.3839	$141.38	$141.40	$141.40
Purchase #4	$13.25	11.507%	$14.7747	$14.77	$14.75	$14.80
Purchase #5	$132.93	10.239%	$146.5407	$146.54	$146.55	$146.50
Purchase #6	$66.36	8.271%	$71.8486	$71.85	$71.85	$71.80
Purchase #7	$185.51	12.820%	$209.2924	$209.29	$209.30	$209.30
7 purchase totals =	$597.87		$663.1314	$663.12	$663.15	$663.10