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	$35.78	12.149%	$40.1269	$40.13	$40.15	$40.10
Purchase #2	$242.97	13.474%	$275.7078	$275.71	$275.70	$275.70
Purchase #3	$166.51	12.478%	$187.2871	$187.29	$187.30	$187.30
Purchase #4	$84.77	13.669%	$96.3572	$96.36	$96.35	$96.40
Purchase #5	$187.39	12.695%	$211.1792	$211.18	$211.20	$211.20
Purchase #6	$90.62	11.292%	$100.8528	$100.85	$100.85	$100.90
Purchase #7	$50.47	9.844%	$55.4383	$55.44	$55.45	$55.40
7 purchase totals =	$858.51		$966.9493	$966.96	$967.00	$967.00