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	$70.59	11.763%	$78.8935	$78.89	$78.90	$78.90
Purchase #2	$141.42	12.518%	$159.123	$159.12	$159.10	$159.10
Purchase #3	$80.59	3.455%	$83.3744	$83.37	$83.35	$83.40
Purchase #4	$182.80	7.766%	$196.9962	$197.00	$197.00	$197.00
Purchase #5	$42.58	10.416%	$47.0151	$47.02	$47.00	$47.00
Purchase #6	$93.29	7.148%	$99.9584	$99.96	$99.95	$100.00
Purchase #7	$51.51	13.743%	$58.589	$58.59	$58.60	$58.60
7 purchase totals =	$662.78		$723.9496	$723.95	$723.90	$724.00