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	$84.34	6.216%	$89.5826	$89.58	$89.60	$89.60
Purchase #2	$168.86	3.826%	$175.3206	$175.32	$175.30	$175.30
Purchase #3	$68.93	13.744%	$78.4037	$78.40	$78.40	$78.40
Purchase #4	$161.47	10.194%	$177.9303	$177.93	$177.95	$177.90
Purchase #5	$41.76	5.189%	$43.9269	$43.93	$43.95	$43.90
Purchase #6	$20.39	5.630%	$21.538	$21.54	$21.55	$21.50
Purchase #7	$30.67	13.422%	$34.7865	$34.79	$34.80	$34.80
7 purchase totals =	$576.42		$621.4886	$621.49	$621.55	$621.40