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	$90.49	11.275%	$100.6927	$100.69	$100.70	$100.70
Purchase #2	$246.34	7.636%	$265.1505	$265.15	$265.15	$265.20
Purchase #3	$48.59	9.493%	$53.2026	$53.20	$53.20	$53.20
Purchase #4	$17.42	7.730%	$18.7666	$18.77	$18.75	$18.80
Purchase #5	$245.52	5.426%	$258.8419	$258.84	$258.85	$258.80
Purchase #6	$144.69	5.208%	$152.2255	$152.23	$152.25	$152.20
Purchase #7	$102.77	6.473%	$109.4223	$109.42	$109.40	$109.40
7 purchase totals =	$895.82		$958.3021	$958.30	$958.30	$958.30