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 $193.95   4.729%   $203.1219   $203.12   $203.10   $203.10  
  Purchase #2 $44.25   3.818%   $45.9395   $45.94   $45.95   $45.90  
  Purchase #3 $158.58   6.762%   $169.3032   $169.30   $169.30   $169.30  
  Purchase #4 $76.87   11.501%   $85.7108   $85.71   $85.70   $85.70  
  Purchase #5 $21.93   10.807%   $24.3   $24.30   $24.30   $24.30  
  Purchase #6 $170.63   5.281%   $179.641   $179.64   $179.65   $179.60  
  Purchase #7 $162.31   8.872%   $176.7101   $176.71   $176.70   $176.70  
  7 purchase totals = $828.52       $884.7265   $884.72   $884.70   $884.60