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 $181.54   6.498%   $193.3365   $193.34   $193.35   $193.30  
  Purchase #2 $57.88   12.410%   $65.0629   $65.06   $65.05   $65.10  
  Purchase #3 $161.33   12.642%   $181.7253   $181.73   $181.75   $181.70  
  Purchase #4 $214.77   3.334%   $221.9304   $221.93   $221.95   $221.90  
  Purchase #5 $77.86   8.767%   $84.686   $84.69   $84.70   $84.70  
  Purchase #6 $229.62   13.183%   $259.8908   $259.89   $259.90   $259.90  
  Purchase #7 $107.31   3.391%   $110.9489   $110.95   $110.95   $110.90  
  7 purchase totals = $1,030.31       $1,117.5808   $1,117.59   $1,117.65   $1,117.50