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	$38.44	11.559%	$42.8833	$42.88	$42.90	$42.90
Purchase #2	$185.61	12.403%	$208.6312	$208.63	$208.65	$208.60
Purchase #3	$92.81	12.481%	$104.3936	$104.39	$104.40	$104.40
Purchase #4	$168.61	8.827%	$183.4932	$183.49	$183.50	$183.50
Purchase #5	$57.87	6.466%	$61.6119	$61.61	$61.60	$61.60
Purchase #6	$162.60	12.735%	$183.3071	$183.31	$183.30	$183.30
Purchase #7	$87.41	9.238%	$95.4849	$95.48	$95.50	$95.50
7 purchase totals =	$793.35		$879.8052	$879.79	$879.85	$879.80