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	$111.82	4.536%	$116.8922	$116.89	$116.90	$116.90
Purchase #2	$83.95	4.167%	$87.4482	$87.45	$87.45	$87.40
Purchase #3	$71.26	9.217%	$77.828	$77.83	$77.85	$77.80
Purchase #4	$177.32	13.769%	$201.7352	$201.74	$201.75	$201.70
Purchase #5	$179.66	4.735%	$188.1669	$188.17	$188.15	$188.20
Purchase #6	$84.77	6.837%	$90.5657	$90.57	$90.55	$90.60
Purchase #7	$42.63	12.275%	$47.8628	$47.86	$47.85	$47.90
7 purchase totals =	$751.41		$810.4990	$810.51	$810.50	$810.50