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	$199.40	9.274%	$217.8924	$217.89	$217.90	$217.90
Purchase #2	$205.55	12.345%	$230.9251	$230.93	$230.95	$230.90
Purchase #3	$140.49	12.757%	$158.4123	$158.41	$158.40	$158.40
Purchase #4	$40.27	5.411%	$42.449	$42.45	$42.45	$42.40
Purchase #5	$83.86	8.520%	$91.0049	$91.00	$91.00	$91.00
Purchase #6	$72.64	12.626%	$81.8115	$81.81	$81.80	$81.80
Purchase #7	$49.44	4.838%	$51.8319	$51.83	$51.85	$51.80
7 purchase totals =	$791.65		$874.3271	$874.32	$874.35	$874.20