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 $58.47   11.735%   $65.3315   $65.33   $65.35   $65.30  
  Purchase #2 $76.83   12.598%   $86.509   $86.51   $86.50   $86.50  
  Purchase #3 $241.34   9.783%   $264.9503   $264.95   $264.95   $265.00  
  Purchase #4 $122.74   12.472%   $138.0481   $138.05   $138.05   $138.00  
  Purchase #5 $159.54   8.474%   $173.0594   $173.06   $173.05   $173.10  
  Purchase #6 $215.31   9.870%   $236.5611   $236.56   $236.55   $236.60  
  Purchase #7 $222.38   7.564%   $239.2008   $239.20   $239.20   $239.20  
  7 purchase totals = $1,096.61       $1,203.6602   $1,203.66   $1,203.65   $1,203.70