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 $189.37   6.276%   $201.2549   $201.25   $201.25   $201.30  
  Purchase #2 $230.56   13.302%   $261.2291   $261.23   $261.25   $261.20  
  Purchase #3 $50.37   13.646%   $57.2435   $57.24   $57.25   $57.20  
  Purchase #4 $245.30   12.617%   $276.2495   $276.25   $276.25   $276.20  
  Purchase #5 $7.36   4.550%   $7.6949   $7.69   $7.70   $7.70  
  Purchase #6 $5.28   8.688%   $5.7387   $5.74   $5.75   $5.70  
  Purchase #7 $191.72   6.688%   $204.5422   $204.54   $204.55   $204.50  
  7 purchase totals = $919.96       $1,013.9528   $1,013.94   $1,014.00   $1,013.80