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 $115.76   8.212%   $125.2662   $125.27   $125.25   $125.30  
  Purchase #2 $184.86   3.721%   $191.7386   $191.74   $191.75   $191.70  
  Purchase #3 $245.47   6.794%   $262.1472   $262.15   $262.15   $262.10  
  Purchase #4 $34.48   6.844%   $36.8398   $36.84   $36.85   $36.80  
  Purchase #5 $230.95   11.217%   $256.8557   $256.86   $256.85   $256.90  
  Purchase #6 $140.61   11.434%   $156.6873   $156.69   $156.70   $156.70  
  Purchase #7 $26.55   5.268%   $27.9487   $27.95   $27.95   $27.90  
  7 purchase totals = $978.68       $1,057.4835   $1,057.50   $1,057.50   $1,057.40