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	$125.37	12.493%	$141.0325	$141.03	$141.05	$141.00
Purchase #2	$196.27	13.387%	$222.5447	$222.54	$222.55	$222.50
Purchase #3	$97.63	11.814%	$109.164	$109.16	$109.15	$109.20
Purchase #4	$39.45	12.417%	$44.3485	$44.35	$44.35	$44.30
Purchase #5	$174.49	4.455%	$182.2635	$182.26	$182.25	$182.30
Purchase #6	$126.81	13.640%	$144.1069	$144.11	$144.10	$144.10
Purchase #7	$132.82	9.789%	$145.8217	$145.82	$145.80	$145.80
7 purchase totals =	$892.84		$989.2818	$989.27	$989.25	$989.20