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	$45.83	9.862%	$50.3498	$50.35	$50.35	$50.30
Purchase #2	$216.73	11.264%	$241.1425	$241.14	$241.15	$241.10
Purchase #3	$127.85	7.489%	$137.4247	$137.42	$137.40	$137.40
Purchase #4	$60.64	11.290%	$67.4863	$67.49	$67.50	$67.50
Purchase #5	$29.55	13.653%	$33.5845	$33.58	$33.60	$33.60
Purchase #6	$201.82	6.688%	$215.3177	$215.32	$215.30	$215.30
Purchase #7	$18.81	3.490%	$19.4665	$19.47	$19.45	$19.50
7 purchase totals =	$701.23		$764.7720	$764.77	$764.75	$764.70