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 $139.57   5.857%   $147.7446   $147.74   $147.75   $147.70  
  Purchase #2 $76.34   11.223%   $84.9076   $84.91   $84.90   $84.90  
  Purchase #3 $90.77   13.175%   $102.7289   $102.73   $102.75   $102.70  
  Purchase #4 $46.63   12.801%   $52.5991   $52.60   $52.60   $52.60  
  Purchase #5 $126.97   13.259%   $143.805   $143.81   $143.80   $143.80  
  Purchase #6 $241.27   7.417%   $259.165   $259.17   $259.15   $259.20  
  Purchase #7 $227.44   11.774%   $254.2188   $254.22   $254.20   $254.20  
  7 purchase totals = $948.99       $1,045.1690   $1,045.18   $1,045.15   $1,045.10