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 $111.79   3.266%   $115.4411   $115.44   $115.45   $115.40  
  Purchase #2 $182.68   8.815%   $198.7832   $198.78   $198.80   $198.80  
  Purchase #3 $152.42   12.808%   $171.942   $171.94   $171.95   $171.90  
  Purchase #4 $248.51   9.410%   $271.8948   $271.89   $271.90   $271.90  
  Purchase #5 $193.36   8.203%   $209.2213   $209.22   $209.20   $209.20  
  Purchase #6 $58.95   3.331%   $60.9136   $60.91   $60.90   $60.90  
  Purchase #7 $215.42   8.625%   $234   $234.00   $234.00   $234.00  
  7 purchase totals = $1,163.13       $1,262.1960   $1,262.18   $1,262.20   $1,262.10