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	$220.99	3.181%	$228.0197	$228.02	$228.00	$228.00
Purchase #2	$177.42	7.189%	$190.1747	$190.17	$190.15	$190.20
Purchase #3	$99.32	9.279%	$108.5359	$108.54	$108.55	$108.50
Purchase #4	$35.55	9.425%	$38.9006	$38.90	$38.90	$38.90
Purchase #5	$107.37	3.667%	$111.3073	$111.31	$111.30	$111.30
Purchase #6	$242.73	8.597%	$263.5975	$263.60	$263.60	$263.60
Purchase #7	$40.45	6.272%	$42.987	$42.99	$43.00	$43.00
7 purchase totals =	$923.83		$983.5227	$983.53	$983.50	$983.50