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 $82.62   5.616%   $87.2599   $87.26   $87.25   $87.30  
  Purchase #2 $99.44   4.855%   $104.2678   $104.27   $104.25   $104.30  
  Purchase #3 $53.38   5.214%   $56.1632   $56.16   $56.15   $56.20  
  Purchase #4 $88.73   8.454%   $96.2312   $96.23   $96.25   $96.20  
  Purchase #5 $123.27   8.680%   $133.9698   $133.97   $133.95   $134.00  
  Purchase #6 $77.33   5.860%   $81.8615   $81.86   $81.85   $81.90  
  Purchase #7 $60.81   4.363%   $63.4631   $63.46   $63.45   $63.50  
  7 purchase totals = $585.58       $623.2165   $623.21   $623.15   $623.40