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	$29.39	6.356%	$31.258	$31.26	$31.25	$31.30
Purchase #2	$108.53	3.392%	$112.2113	$112.21	$112.20	$112.20
Purchase #3	$54.43	13.594%	$61.8292	$61.83	$61.85	$61.80
Purchase #4	$64.84	10.620%	$71.726	$71.73	$71.75	$71.70
Purchase #5	$238.29	12.426%	$267.8999	$267.90	$267.90	$267.90
Purchase #6	$107.94	10.483%	$119.2554	$119.26	$119.25	$119.30
Purchase #7	$19.58	9.266%	$21.3943	$21.39	$21.40	$21.40
7 purchase totals =	$623.00		$685.5741	$685.58	$685.60	$685.60