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 $59.69   12.624%   $67.2253   $67.23   $67.25   $67.20  
  Purchase #2 $167.96   6.768%   $179.3275   $179.33   $179.35   $179.30  
  Purchase #3 $61.83   8.338%   $66.9854   $66.99   $67.00   $67.00  
  Purchase #4 $137.43   12.486%   $154.5895   $154.59   $154.60   $154.60  
  Purchase #5 $188.86   4.556%   $197.4645   $197.46   $197.45   $197.50  
  Purchase #6 $70.41   7.681%   $75.8182   $75.82   $75.80   $75.80  
  Purchase #7 $67.49   4.858%   $70.7687   $70.77   $70.75   $70.80  
  7 purchase totals = $753.67       $812.1791   $812.19   $812.20   $812.20