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 $208.93   9.682%   $229.1586   $229.16   $229.15   $229.20  
  Purchase #2 $162.77   9.578%   $178.3601   $178.36   $178.35   $178.40  
  Purchase #3 $73.62   11.285%   $81.928   $81.93   $81.95   $81.90  
  Purchase #4 $88.43   9.616%   $96.9334   $96.93   $96.95   $96.90  
  Purchase #5 $232.68   11.729%   $259.971   $259.97   $259.95   $260.00  
  Purchase #6 $63.47   13.354%   $71.9458   $71.95   $71.95   $71.90  
  Purchase #7 $108.47   4.478%   $113.3273   $113.33   $113.35   $113.30  
  7 purchase totals = $938.37       $1,031.6242   $1,031.63   $1,031.65   $1,031.60