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 $42.83   9.121%   $46.7365   $46.74   $46.75   $46.70  
  Purchase #2 $149.98   10.790%   $166.1628   $166.16   $166.15   $166.20  
  Purchase #3 $46.49   6.794%   $49.6485   $49.65   $49.65   $49.60  
  Purchase #4 $241.83   3.721%   $250.8285   $250.83   $250.85   $250.80  
  Purchase #5 $125.98   12.431%   $141.6406   $141.64   $141.65   $141.60  
  Purchase #6 $136.44   7.163%   $146.2132   $146.21   $146.20   $146.20  
  Purchase #7 $30.77   3.834%   $31.9497   $31.95   $31.95   $31.90  
  7 purchase totals = $774.32       $833.1798   $833.18   $833.20   $833.00