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	$33.50	12.236%	$37.5991	$37.60	$37.60	$37.60
Purchase #2	$50.80	10.421%	$56.0939	$56.09	$56.10	$56.10
Purchase #3	$66.40	7.536%	$71.4039	$71.40	$71.40	$71.40
Purchase #4	$166.77	7.820%	$179.8114	$179.81	$179.80	$179.80
Purchase #5	$43.61	7.304%	$46.7953	$46.80	$46.80	$46.80
Purchase #6	$225.81	5.553%	$238.3492	$238.35	$238.35	$238.30
Purchase #7	$24.95	13.795%	$28.3919	$28.39	$28.40	$28.40
7 purchase totals =	$611.84		$658.4447	$658.44	$658.45	$658.40