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 $205.82   8.854%   $224.0433   $224.04   $224.05   $224.00  
  Purchase #2 $171.90   9.513%   $188.2528   $188.25   $188.25   $188.30  
  Purchase #3 $54.31   11.824%   $60.7316   $60.73   $60.75   $60.70  
  Purchase #4 $184.60   6.194%   $196.0341   $196.03   $196.05   $196.00  
  Purchase #5 $176.65   9.632%   $193.6649   $193.66   $193.65   $193.70  
  Purchase #6 $146.65   9.389%   $160.419   $160.42   $160.40   $160.40  
  Purchase #7 $195.91   6.192%   $208.0407   $208.04   $208.05   $208.00  
  7 purchase totals = $1,135.84       $1,231.1864   $1,231.17   $1,231.20   $1,231.10