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 $25.92   3.232%   $26.7577   $26.76   $26.75   $26.80  
  Purchase #2 $214.39   4.691%   $224.447   $224.45   $224.45   $224.40  
  Purchase #3 $150.61   10.628%   $166.6168   $166.62   $166.60   $166.60  
  Purchase #4 $179.71   3.361%   $185.7501   $185.75   $185.75   $185.80  
  Purchase #5 $28.58   6.118%   $30.3285   $30.33   $30.35   $30.30  
  Purchase #6 $88.51   13.231%   $100.2208   $100.22   $100.20   $100.20  
  Purchase #7 $122.28   3.264%   $126.2712   $126.27   $126.25   $126.30  
  7 purchase totals = $810.00       $860.3921   $860.40   $860.35   $860.40