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 $244.57   13.265%   $277.0122   $277.01   $277.00   $277.00  
  Purchase #2 $86.98   7.412%   $93.427   $93.43   $93.45   $93.40  
  Purchase #3 $233.36   7.520%   $250.9087   $250.91   $250.90   $250.90  
  Purchase #4 $242.64   6.136%   $257.5284   $257.53   $257.55   $257.50  
  Purchase #5 $15.64   9.165%   $17.0734   $17.07   $17.05   $17.10  
  Purchase #6 $217.98   3.225%   $225.0099   $225.01   $225.00   $225.00  
  Purchase #7 $12.48   13.594%   $14.1765   $14.18   $14.20   $14.20  
  7 purchase totals = $1,053.65       $1,135.1361   $1,135.14   $1,135.15   $1,135.10