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	$73.65	9.274%	$80.4803	$80.48	$80.50	$80.50
Purchase #2	$241.48	5.679%	$255.1936	$255.19	$255.20	$255.20
Purchase #3	$84.47	7.309%	$90.6439	$90.64	$90.65	$90.60
Purchase #4	$104.40	11.732%	$116.6482	$116.65	$116.65	$116.60
Purchase #5	$40.85	5.775%	$43.2091	$43.21	$43.20	$43.20
Purchase #6	$157.39	4.855%	$165.0313	$165.03	$165.05	$165.00
Purchase #7	$89.26	4.768%	$93.5159	$93.52	$93.50	$93.50
7 purchase totals =	$791.50		$844.7223	$844.72	$844.75	$844.60