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 $208.35   4.321%   $217.3528   $217.35   $217.35   $217.40  
  Purchase #2 $186.75   8.124%   $201.9216   $201.92   $201.90   $201.90  
  Purchase #3 $131.40   8.753%   $142.9014   $142.90   $142.90   $142.90  
  Purchase #4 $250.37   4.198%   $260.8805   $260.88   $260.90   $260.90  
  Purchase #5 $138.41   5.686%   $146.28   $146.28   $146.30   $146.30  
  Purchase #6 $230.26   7.171%   $246.7719   $246.77   $246.75   $246.80  
  Purchase #7 $55.68   4.535%   $58.2051   $58.21   $58.20   $58.20  
  7 purchase totals = $1,201.22       $1,274.3133   $1,274.31   $1,274.30   $1,274.40