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 $97.92   10.484%   $108.1859   $108.19   $108.20   $108.20  
  Purchase #2 $102.40   6.611%   $109.1697   $109.17   $109.15   $109.20  
  Purchase #3 $242.71   6.153%   $257.6439   $257.64   $257.65   $257.60  
  Purchase #4 $30.29   4.180%   $31.5561   $31.56   $31.55   $31.60  
  Purchase #5 $240.38   8.350%   $260.4517   $260.45   $260.45   $260.50  
  Purchase #6 $185.32   10.437%   $204.6618   $204.66   $204.65   $204.70  
  Purchase #7 $141.76   11.533%   $158.1092   $158.11   $158.10   $158.10  
  7 purchase totals = $1,040.78       $1,129.7783   $1,129.78   $1,129.75   $1,129.90