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	$130.47	9.222%	$142.5019	$142.50	$142.50	$142.50
Purchase #2	$6.68	12.406%	$7.5087	$7.51	$7.50	$7.50
Purchase #3	$114.53	10.789%	$126.8866	$126.89	$126.90	$126.90
Purchase #4	$124.64	13.567%	$141.5499	$141.55	$141.55	$141.50
Purchase #5	$89.40	9.704%	$98.0754	$98.08	$98.10	$98.10
Purchase #6	$44.86	5.635%	$47.3879	$47.39	$47.40	$47.40
Purchase #7	$94.58	5.599%	$99.8755	$99.88	$99.90	$99.90
7 purchase totals =	$605.16		$663.7859	$663.80	$663.85	$663.80