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 $47.77   12.855%   $53.9108   $53.91   $53.90   $53.90  
  Purchase #2 $207.76   10.695%   $229.9799   $229.98   $230.00   $230.00  
  Purchase #3 $125.59   7.330%   $134.7957   $134.80   $134.80   $134.80  
  Purchase #4 $203.75   6.557%   $217.1099   $217.11   $217.10   $217.10  
  Purchase #5 $20.27   7.602%   $21.8109   $21.81   $21.80   $21.80  
  Purchase #6 $239.41   10.766%   $265.1849   $265.18   $265.20   $265.20  
  Purchase #7 $20.97   12.456%   $23.582   $23.58   $23.60   $23.60  
  7 purchase totals = $865.52       $946.3741   $946.37   $946.40   $946.40