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	$81.82	10.429%	$90.353	$90.35	$90.35	$90.40
Purchase #2	$145.40	7.142%	$155.7845	$155.78	$155.80	$155.80
Purchase #3	$99.62	11.465%	$111.0414	$111.04	$111.05	$111.00
Purchase #4	$124.46	5.564%	$131.385	$131.39	$131.40	$131.40
Purchase #5	$121.56	8.192%	$131.5182	$131.52	$131.50	$131.50
Purchase #6	$117.90	11.630%	$131.6118	$131.61	$131.60	$131.60
Purchase #7	$135.25	9.441%	$148.019	$148.02	$148.00	$148.00
7 purchase totals =	$826.01		$899.7129	$899.71	$899.70	$899.70