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 $54.36   11.605%   $60.6685   $60.67   $60.65   $60.70  
  Purchase #2 $196.76   8.843%   $214.1595   $214.16   $214.15   $214.20  
  Purchase #3 $98.97   8.436%   $107.3191   $107.32   $107.30   $107.30  
  Purchase #4 $151.54   9.482%   $165.909   $165.91   $165.90   $165.90  
  Purchase #5 $144.63   7.387%   $155.3138   $155.31   $155.30   $155.30  
  Purchase #6 $171.46   13.125%   $193.9641   $193.96   $193.95   $194.00  
  Purchase #7 $113.51   10.839%   $125.8133   $125.81   $125.80   $125.80  
  7 purchase totals = $931.23       $1,023.1473   $1,023.14   $1,023.05   $1,023.20