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 $228.78   7.859%   $246.7598   $246.76   $246.75   $246.80  
  Purchase #2 $144.35   3.676%   $149.6563   $149.66   $149.65   $149.70  
  Purchase #3 $127.36   10.175%   $140.3189   $140.32   $140.30   $140.30  
  Purchase #4 $24.55   5.601%   $25.925   $25.93   $25.95   $25.90  
  Purchase #5 $67.95   7.672%   $73.1631   $73.16   $73.15   $73.20  
  Purchase #6 $22.79   9.213%   $24.8896   $24.89   $24.90   $24.90  
  Purchase #7 $189.61   6.264%   $201.4872   $201.49   $201.50   $201.50  
  7 purchase totals = $805.39       $862.1999   $862.21   $862.20   $862.30