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	$87.69	3.285%	$90.5706	$90.57	$90.55	$90.60
Purchase #2	$33.29	12.765%	$37.5395	$37.54	$37.55	$37.50
Purchase #3	$134.89	4.259%	$140.635	$140.64	$140.65	$140.60
Purchase #4	$130.78	7.110%	$140.0785	$140.08	$140.10	$140.10
Purchase #5	$186.38	7.550%	$200.4517	$200.45	$200.45	$200.50
Purchase #6	$50.42	7.547%	$54.2252	$54.23	$54.25	$54.20
Purchase #7	$190.39	13.619%	$216.3192	$216.32	$216.30	$216.30
7 purchase totals =	$813.84		$879.8197	$879.83	$879.85	$879.80