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	$40.88	3.372%	$42.2585	$42.26	$42.25	$42.30
Purchase #2	$36.84	7.359%	$39.5511	$39.55	$39.55	$39.60
Purchase #3	$89.38	6.806%	$95.4632	$95.46	$95.45	$95.50
Purchase #4	$82.40	8.662%	$89.5375	$89.54	$89.55	$89.50
Purchase #5	$200.54	12.426%	$225.4591	$225.46	$225.45	$225.50
Purchase #6	$213.88	10.758%	$236.8892	$236.89	$236.90	$236.90
Purchase #7	$199.77	10.178%	$220.1026	$220.10	$220.10	$220.10
7 purchase totals =	$863.69		$949.2612	$949.26	$949.25	$949.40