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	$40.67	4.402%	$42.4603	$42.46	$42.45	$42.50
Purchase #2	$156.26	9.453%	$171.0313	$171.03	$171.05	$171.00
Purchase #3	$175.93	3.236%	$181.6231	$181.62	$181.60	$181.60
Purchase #4	$29.64	12.641%	$33.3868	$33.39	$33.40	$33.40
Purchase #5	$168.44	9.155%	$183.8607	$183.86	$183.85	$183.90
Purchase #6	$225.34	6.460%	$239.897	$239.90	$239.90	$239.90
Purchase #7	$125.39	12.682%	$141.292	$141.29	$141.30	$141.30
7 purchase totals =	$921.67		$993.5512	$993.55	$993.55	$993.60