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	$102.54	11.750%	$114.5885	$114.59	$114.60	$114.60
Purchase #2	$141.72	13.387%	$160.6921	$160.69	$160.70	$160.70
Purchase #3	$237.91	9.578%	$260.697	$260.70	$260.70	$260.70
Purchase #4	$213.36	13.710%	$242.6117	$242.61	$242.60	$242.60
Purchase #5	$42.68	7.362%	$45.8221	$45.82	$45.80	$45.80
Purchase #6	$62.97	4.622%	$65.8805	$65.88	$65.90	$65.90
Purchase #7	$99.27	4.310%	$103.5485	$103.55	$103.55	$103.50
7 purchase totals =	$900.45		$993.8404	$993.84	$993.85	$993.80