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 $208.75   7.754%   $224.9365   $224.94   $224.95   $224.90  
  Purchase #2 $186.32   9.328%   $203.6999   $203.70   $203.70   $203.70  
  Purchase #3 $104.44   9.346%   $114.201   $114.20   $114.20   $114.20  
  Purchase #4 $203.84   13.719%   $231.8048   $231.80   $231.80   $231.80  
  Purchase #5 $203.89   11.303%   $226.9357   $226.94   $226.95   $226.90  
  Purchase #6 $179.55   8.670%   $195.117   $195.12   $195.10   $195.10  
  Purchase #7 $65.38   12.683%   $73.6721   $73.67   $73.65   $73.70  
  7 purchase totals = $1,152.17       $1,270.3670   $1,270.37   $1,270.35   $1,270.30