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 $182.29   10.507%   $201.4432   $201.44   $201.45   $201.40  
  Purchase #2 $240.86   13.543%   $273.4797   $273.48   $273.50   $273.50  
  Purchase #3 $162.63   8.653%   $176.7024   $176.70   $176.70   $176.70  
  Purchase #4 $230.47   9.723%   $252.8786   $252.88   $252.90   $252.90  
  Purchase #5 $184.26   10.457%   $203.5281   $203.53   $203.55   $203.50  
  Purchase #6 $54.47   6.276%   $57.8885   $57.89   $57.90   $57.90  
  Purchase #7 $121.82   13.296%   $138.0172   $138.02   $138.00   $138.00  
  7 purchase totals = $1,176.80       $1,303.9377   $1,303.94   $1,304.00   $1,303.90