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	$157.90	3.119%	$162.8249	$162.82	$162.80	$162.80
Purchase #2	$135.51	3.233%	$139.891	$139.89	$139.90	$139.90
Purchase #3	$73.49	9.511%	$80.4796	$80.48	$80.50	$80.50
Purchase #4	$111.61	13.175%	$126.3146	$126.31	$126.30	$126.30
Purchase #5	$103.78	12.419%	$116.6684	$116.67	$116.65	$116.70
Purchase #6	$164.53	6.168%	$174.6782	$174.68	$174.70	$174.70
Purchase #7	$66.51	5.576%	$70.2186	$70.22	$70.20	$70.20
7 purchase totals =	$813.33		$871.0753	$871.07	$871.05	$871.10