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	$105.44	13.232%	$119.3918	$119.39	$119.40	$119.40
Purchase #2	$42.64	11.656%	$47.6101	$47.61	$47.60	$47.60
Purchase #3	$48.66	13.855%	$55.4018	$55.40	$55.40	$55.40
Purchase #4	$126.60	3.814%	$131.4285	$131.43	$131.45	$131.40
Purchase #5	$142.45	4.720%	$149.1736	$149.17	$149.15	$149.20
Purchase #6	$118.79	4.655%	$124.3197	$124.32	$124.30	$124.30
Purchase #7	$150.83	3.805%	$156.5691	$156.57	$156.55	$156.60
7 purchase totals =	$735.41		$783.8946	$783.89	$783.85	$783.90