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	$83.78	7.613%	$90.1582	$90.16	$90.15	$90.20
Purchase #2	$243.81	9.801%	$267.7058	$267.71	$267.70	$267.70
Purchase #3	$32.93	11.517%	$36.7225	$36.72	$36.70	$36.70
Purchase #4	$105.75	3.817%	$109.7865	$109.79	$109.80	$109.80
Purchase #5	$63.86	4.828%	$66.9432	$66.94	$66.95	$66.90
Purchase #6	$213.56	5.290%	$224.8573	$224.86	$224.85	$224.90
Purchase #7	$123.26	12.532%	$138.7069	$138.71	$138.70	$138.70
7 purchase totals =	$866.95		$934.8804	$934.89	$934.85	$934.90