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 $239.44   12.426%   $269.1928   $269.19   $269.20   $269.20  
  Purchase #2 $82.64   13.359%   $93.6799   $93.68   $93.70   $93.70  
  Purchase #3 $133.84   9.716%   $146.8439   $146.84   $146.85   $146.80  
  Purchase #4 $179.95   4.221%   $187.5457   $187.55   $187.55   $187.50  
  Purchase #5 $203.94   8.704%   $221.6909   $221.69   $221.70   $221.70  
  Purchase #6 $191.59   4.182%   $199.6023   $199.60   $199.60   $199.60  
  Purchase #7 $114.31   6.570%   $121.8202   $121.82   $121.80   $121.80  
  7 purchase totals = $1,145.71       $1,240.3757   $1,240.37   $1,240.40   $1,240.30