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	$145.96	7.414%	$156.7815	$156.78	$156.80	$156.80
Purchase #2	$40.58	12.283%	$45.5644	$45.56	$45.55	$45.60
Purchase #3	$39.89	6.672%	$42.5515	$42.55	$42.55	$42.60
Purchase #4	$183.89	13.340%	$208.4209	$208.42	$208.40	$208.40
Purchase #5	$102.91	12.859%	$116.1432	$116.14	$116.15	$116.10
Purchase #6	$107.41	13.132%	$121.5151	$121.52	$121.50	$121.50
Purchase #7	$52.83	8.636%	$57.3924	$57.39	$57.40	$57.40
7 purchase totals =	$673.47		$748.3690	$748.36	$748.35	$748.40