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	$131.84	9.546%	$144.4254	$144.43	$144.45	$144.40
Purchase #2	$138.45	4.670%	$144.9156	$144.92	$144.90	$144.90
Purchase #3	$60.43	8.582%	$65.6161	$65.62	$65.60	$65.60
Purchase #4	$133.67	8.402%	$144.901	$144.90	$144.90	$144.90
Purchase #5	$168.73	12.162%	$189.2509	$189.25	$189.25	$189.30
Purchase #6	$20.39	7.366%	$21.8919	$21.89	$21.90	$21.90
Purchase #7	$180.98	11.324%	$201.4742	$201.47	$201.45	$201.50
7 purchase totals =	$834.49		$912.4751	$912.48	$912.45	$912.50