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 $47.33   10.797%   $52.4402   $52.44   $52.45   $52.40  
  Purchase #2 $94.64   8.385%   $102.5756   $102.58   $102.60   $102.60  
  Purchase #3 $110.66   8.597%   $120.1734   $120.17   $120.15   $120.20  
  Purchase #4 $175.78   7.480%   $188.9283   $188.93   $188.95   $188.90  
  Purchase #5 $118.73   7.334%   $127.4377   $127.44   $127.45   $127.40  
  Purchase #6 $230.46   12.468%   $259.1938   $259.19   $259.20   $259.20  
  Purchase #7 $60.46   10.562%   $66.8458   $66.85   $66.85   $66.80  
  7 purchase totals = $838.06       $917.5948   $917.60   $917.65   $917.50