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 $217.98   13.599%   $247.6231   $247.62   $247.60   $247.60  
  Purchase #2 $217.69   10.457%   $240.4538   $240.45   $240.45   $240.50  
  Purchase #3 $119.73   4.629%   $125.2723   $125.27   $125.25   $125.30  
  Purchase #4 $168.67   3.280%   $174.2024   $174.20   $174.20   $174.20  
  Purchase #5 $26.71   6.633%   $28.4817   $28.48   $28.50   $28.50  
  Purchase #6 $72.40   8.415%   $78.4925   $78.49   $78.50   $78.50  
  Purchase #7 $126.78   6.221%   $134.667   $134.67   $134.65   $134.70  
  7 purchase totals = $949.96       $1,029.1928   $1,029.18   $1,029.15   $1,029.30