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 $65.56   9.232%   $71.6125   $71.61   $71.60   $71.60  
  Purchase #2 $108.68   9.225%   $118.7057   $118.71   $118.70   $118.70  
  Purchase #3 $72.97   4.241%   $76.0647   $76.06   $76.05   $76.10  
  Purchase #4 $198.95   8.417%   $215.6956   $215.70   $215.70   $215.70  
  Purchase #5 $132.79   6.651%   $141.6219   $141.62   $141.60   $141.60  
  Purchase #6 $162.45   8.874%   $176.8658   $176.87   $176.85   $176.90  
  Purchase #7 $180.61   6.591%   $192.514   $192.51   $192.50   $192.50  
  7 purchase totals = $922.01       $993.0802   $993.08   $993.00   $993.10