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 $60.79   13.459%   $68.9717   $68.97   $68.95   $69.00  
  Purchase #2 $126.48   12.157%   $141.8562   $141.86   $141.85   $141.90  
  Purchase #3 $30.39   8.349%   $32.9273   $32.93   $32.95   $32.90  
  Purchase #4 $104.58   13.284%   $118.4724   $118.47   $118.45   $118.50  
  Purchase #5 $190.60   12.465%   $214.3583   $214.36   $214.35   $214.40  
  Purchase #6 $202.41   8.271%   $219.1513   $219.15   $219.15   $219.20  
  Purchase #7 $77.57   8.227%   $83.9517   $83.95   $83.95   $84.00  
  7 purchase totals = $792.82       $879.6889   $879.69   $879.65   $879.90