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 $164.56   6.648%   $175.4999   $175.50   $175.50   $175.50  
  Purchase #2 $212.56   12.740%   $239.6401   $239.64   $239.65   $239.60  
  Purchase #3 $201.26   8.347%   $218.0592   $218.06   $218.05   $218.10  
  Purchase #4 $228.78   11.452%   $254.9799   $254.98   $255.00   $255.00  
  Purchase #5 $240.58   5.836%   $254.6202   $254.62   $254.60   $254.60  
  Purchase #6 $7.32   4.240%   $7.6304   $7.63   $7.65   $7.60  
  Purchase #7 $235.63   10.865%   $261.2312   $261.23   $261.25   $261.20  
  7 purchase totals = $1,290.69       $1,411.6609   $1,411.66   $1,411.70   $1,411.60