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	$83.37	8.607%	$90.5457	$90.55	$90.55	$90.50
Purchase #2	$166.34	9.675%	$182.4334	$182.43	$182.45	$182.40
Purchase #3	$208.62	10.690%	$230.9215	$230.92	$230.90	$230.90
Purchase #4	$28.46	12.126%	$31.9111	$31.91	$31.90	$31.90
Purchase #5	$174.81	7.451%	$187.8351	$187.84	$187.85	$187.80
Purchase #6	$189.96	13.830%	$216.2315	$216.23	$216.25	$216.20
Purchase #7	$18.66	3.578%	$19.3277	$19.33	$19.35	$19.30
7 purchase totals =	$870.22		$959.2060	$959.21	$959.25	$959.00