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	$155.47	8.386%	$168.5077	$168.51	$168.50	$168.50
Purchase #2	$188.39	13.440%	$213.7096	$213.71	$213.70	$213.70
Purchase #3	$57.65	3.533%	$59.6868	$59.69	$59.70	$59.70
Purchase #4	$36.49	10.630%	$40.3689	$40.37	$40.35	$40.40
Purchase #5	$107.83	8.432%	$116.9222	$116.92	$116.90	$116.90
Purchase #6	$97.42	8.452%	$105.6539	$105.65	$105.65	$105.70
Purchase #7	$126.45	3.695%	$131.1223	$131.12	$131.10	$131.10
7 purchase totals =	$769.70		$835.9714	$835.97	$835.90	$836.00