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	$177.89	3.372%	$183.8885	$183.89	$183.90	$183.90
Purchase #2	$119.63	9.671%	$131.1994	$131.20	$131.20	$131.20
Purchase #3	$99.73	13.860%	$113.5526	$113.55	$113.55	$113.60
Purchase #4	$163.66	4.398%	$170.8578	$170.86	$170.85	$170.90
Purchase #5	$77.55	9.694%	$85.0677	$85.07	$85.05	$85.10
Purchase #6	$141.63	10.350%	$156.2887	$156.29	$156.30	$156.30
Purchase #7	$109.43	7.406%	$117.5344	$117.53	$117.55	$117.50
7 purchase totals =	$889.52		$958.3891	$958.39	$958.40	$958.50