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 $65.77   3.858%   $68.3074   $68.31   $68.30   $68.30  
  Purchase #2 $189.79   13.280%   $214.9941   $214.99   $215.00   $215.00  
  Purchase #3 $242.67   6.515%   $258.48   $258.48   $258.50   $258.50  
  Purchase #4 $227.34   3.237%   $234.699   $234.70   $234.70   $234.70  
  Purchase #5 $156.49   3.342%   $161.7199   $161.72   $161.70   $161.70  
  Purchase #6 $228.93   13.436%   $259.689   $259.69   $259.70   $259.70  
  Purchase #7 $92.49   10.705%   $102.3911   $102.39   $102.40   $102.40  
  7 purchase totals = $1,203.48       $1,300.2805   $1,300.28   $1,300.30   $1,300.30