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 $239.59   12.171%   $268.7505   $268.75   $268.75   $268.80  
  Purchase #2 $82.54   5.349%   $86.9551   $86.96   $86.95   $87.00  
  Purchase #3 $205.30   8.167%   $222.0669   $222.07   $222.05   $222.10  
  Purchase #4 $126.36   9.205%   $137.9914   $137.99   $138.00   $138.00  
  Purchase #5 $203.25   4.841%   $213.0893   $213.09   $213.10   $213.10  
  Purchase #6 $232.54   6.129%   $246.7924   $246.79   $246.80   $246.80  
  Purchase #7 $112.42   11.869%   $125.7631   $125.76   $125.75   $125.80  
  7 purchase totals = $1,202.00       $1,301.4087   $1,301.41   $1,301.40   $1,301.60