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 $131.35   11.734%   $146.7626   $146.76   $146.75   $146.80  
  Purchase #2 $173.86   4.302%   $181.3395   $181.34   $181.35   $181.30  
  Purchase #3 $55.87   8.446%   $60.5888   $60.59   $60.60   $60.60  
  Purchase #4 $163.97   3.167%   $169.1629   $169.16   $169.15   $169.20  
  Purchase #5 $200.76   11.432%   $223.7109   $223.71   $223.70   $223.70  
  Purchase #6 $175.46   13.790%   $199.6559   $199.66   $199.65   $199.70  
  Purchase #7 $58.32   7.153%   $62.4916   $62.49   $62.50   $62.50  
  7 purchase totals = $959.59       $1,043.7122   $1,043.71   $1,043.70   $1,043.80