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 $94.37   8.267%   $102.1716   $102.17   $102.15   $102.20  
  Purchase #2 $159.70   8.858%   $173.8462   $173.85   $173.85   $173.80  
  Purchase #3 $68.72   12.622%   $77.3938   $77.39   $77.40   $77.40  
  Purchase #4 $241.71   5.467%   $254.9243   $254.92   $254.90   $254.90  
  Purchase #5 $130.65   12.136%   $146.5057   $146.51   $146.50   $146.50  
  Purchase #6 $208.29   13.833%   $237.1028   $237.10   $237.10   $237.10  
  Purchase #7 $187.34   5.210%   $197.1004   $197.10   $197.10   $197.10  
  7 purchase totals = $1,090.78       $1,189.0448   $1,189.04   $1,189.00   $1,189.00