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	$100.56	13.245%	$113.8792	$113.88	$113.90	$113.90
Purchase #2	$157.40	6.620%	$167.8199	$167.82	$167.80	$167.80
Purchase #3	$241.37	7.453%	$259.3593	$259.36	$259.35	$259.40
Purchase #4	$164.32	6.843%	$175.5644	$175.56	$175.55	$175.60
Purchase #5	$66.62	6.863%	$71.1921	$71.19	$71.20	$71.20
Purchase #6	$136.59	9.872%	$150.0742	$150.07	$150.05	$150.10
Purchase #7	$84.53	7.532%	$90.8968	$90.90	$90.90	$90.90
7 purchase totals =	$951.39		$1,028.7859	$1,028.78	$1,028.75	$1,028.90