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 $247.75   11.803%   $276.9919   $276.99   $277.00   $277.00  
  Purchase #2 $93.93   8.592%   $102.0005   $102.00   $102.00   $102.00  
  Purchase #3 $186.71   10.347%   $206.0289   $206.03   $206.05   $206.00  
  Purchase #4 $33.80   10.210%   $37.251   $37.25   $37.25   $37.30  
  Purchase #5 $17.56   5.683%   $18.5579   $18.56   $18.55   $18.60  
  Purchase #6 $33.77   5.265%   $35.548   $35.55   $35.55   $35.50  
  Purchase #7 $53.78   10.615%   $59.4887   $59.49   $59.50   $59.50  
  7 purchase totals = $667.30       $735.8669   $735.87   $735.90   $735.90