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 $106.95   13.678%   $121.5786   $121.58   $121.60   $121.60  
  Purchase #2 $119.47   8.604%   $129.7492   $129.75   $129.75   $129.70  
  Purchase #3 $81.95   6.139%   $86.9809   $86.98   $87.00   $87.00  
  Purchase #4 $231.64   12.285%   $260.097   $260.10   $260.10   $260.10  
  Purchase #5 $243.54   6.783%   $260.0593   $260.06   $260.05   $260.10  
  Purchase #6 $246.28   5.294%   $259.3181   $259.32   $259.30   $259.30  
  Purchase #7 $201.79   7.441%   $216.8052   $216.81   $216.80   $216.80  
  7 purchase totals = $1,231.62       $1,334.5883   $1,334.60   $1,334.60   $1,334.60