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	$169.41	12.208%	$190.0916	$190.09	$190.10	$190.10
Purchase #2	$196.60	11.122%	$218.4659	$218.47	$218.45	$218.50
Purchase #3	$128.52	12.180%	$144.1737	$144.17	$144.15	$144.20
Purchase #4	$241.44	13.423%	$273.8485	$273.85	$273.85	$273.80
Purchase #5	$44.48	6.446%	$47.3472	$47.35	$47.35	$47.30
Purchase #6	$128.41	4.600%	$134.3169	$134.32	$134.30	$134.30
Purchase #7	$32.29	6.715%	$34.4583	$34.46	$34.45	$34.50
7 purchase totals =	$941.15		$1,042.7021	$1,042.71	$1,042.65	$1,042.70