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 $62.53   3.126%   $64.4847   $64.48   $64.50   $64.50  
  Purchase #2 $225.68   3.309%   $233.1478   $233.15   $233.15   $233.10  
  Purchase #3 $112.93   8.818%   $122.8882   $122.89   $122.90   $122.90  
  Purchase #4 $96.78   7.659%   $104.1924   $104.19   $104.20   $104.20  
  Purchase #5 $32.97   5.846%   $34.8974   $34.90   $34.90   $34.90  
  Purchase #6 $200.83   8.819%   $218.5412   $218.54   $218.55   $218.50  
  Purchase #7 $74.27   5.261%   $78.1773   $78.18   $78.20   $78.20  
  7 purchase totals = $805.99       $856.3290   $856.33   $856.40   $856.30