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	$98.66	10.296%	$108.818	$108.82	$108.80	$108.80
Purchase #2	$59.55	13.811%	$67.7745	$67.77	$67.75	$67.80
Purchase #3	$250.54	4.322%	$261.3683	$261.37	$261.35	$261.40
Purchase #4	$29.72	3.845%	$30.8627	$30.86	$30.85	$30.90
Purchase #5	$42.70	5.859%	$45.2018	$45.20	$45.20	$45.20
Purchase #6	$89.73	12.807%	$101.2217	$101.22	$101.20	$101.20
Purchase #7	$47.47	8.406%	$51.4603	$51.46	$51.45	$51.50
7 purchase totals =	$618.37		$666.7073	$666.70	$666.60	$666.80