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 $36.61   13.149%   $41.4238   $41.42   $41.40   $41.40  
  Purchase #2 $242.97   7.763%   $261.8318   $261.83   $261.85   $261.80  
  Purchase #3 $80.86   3.763%   $83.9028   $83.90   $83.90   $83.90  
  Purchase #4 $59.93   3.251%   $61.8783   $61.88   $61.90   $61.90  
  Purchase #5 $8.41   7.278%   $9.0221   $9.02   $9.00   $9.00  
  Purchase #6 $61.36   3.336%   $63.407   $63.41   $63.40   $63.40  
  Purchase #7 $220.63   6.341%   $234.6201   $234.62   $234.60   $234.60  
  7 purchase totals = $710.77       $756.0859   $756.08   $756.05   $756.00