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 $142.73   9.737%   $156.6276   $156.63   $156.65   $156.60  
  Purchase #2 $75.92   6.317%   $80.7159   $80.72   $80.70   $80.70  
  Purchase #3 $144.42   4.356%   $150.7109   $150.71   $150.70   $150.70  
  Purchase #4 $86.41   3.792%   $89.6867   $89.69   $89.70   $89.70  
  Purchase #5 $78.44   7.275%   $84.1465   $84.15   $84.15   $84.10  
  Purchase #6 $190.78   13.795%   $217.0981   $217.10   $217.10   $217.10  
  Purchase #7 $25.75   11.356%   $28.6742   $28.67   $28.65   $28.70  
  7 purchase totals = $744.45       $807.6599   $807.67   $807.65   $807.60