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 $64.46   10.373%   $71.1464   $71.15   $71.15   $71.10  
  Purchase #2 $191.87   13.697%   $218.1504   $218.15   $218.15   $218.20  
  Purchase #3 $167.49   12.611%   $188.6122   $188.61   $188.60   $188.60  
  Purchase #4 $195.89   9.591%   $214.6778   $214.68   $214.70   $214.70  
  Purchase #5 $14.89   8.143%   $16.1025   $16.10   $16.10   $16.10  
  Purchase #6 $167.82   3.758%   $174.1267   $174.13   $174.15   $174.10  
  Purchase #7 $196.51   12.376%   $220.8301   $220.83   $220.85   $220.80  
  7 purchase totals = $998.93       $1,103.6461   $1,103.65   $1,103.70   $1,103.60