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 $58.84   6.351%   $62.5769   $62.58   $62.60   $62.60  
  Purchase #2 $226.54   3.554%   $234.5912   $234.59   $234.60   $234.60  
  Purchase #3 $85.78   7.462%   $92.1809   $92.18   $92.20   $92.20  
  Purchase #4 $126.66   7.351%   $135.9708   $135.97   $135.95   $136.00  
  Purchase #5 $247.97   7.268%   $265.9925   $265.99   $266.00   $266.00  
  Purchase #6 $35.74   6.255%   $37.9755   $37.98   $38.00   $38.00  
  Purchase #7 $134.89   8.776%   $146.7279   $146.73   $146.75   $146.70  
  7 purchase totals = $916.42       $976.0157   $976.02   $976.10   $976.10