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 $69.85   5.534%   $73.7155   $73.72   $73.70   $73.70  
  Purchase #2 $190.60   11.154%   $211.8595   $211.86   $211.85   $211.90  
  Purchase #3 $62.89   3.480%   $65.0786   $65.08   $65.10   $65.10  
  Purchase #4 $146.46   11.596%   $163.4435   $163.44   $163.45   $163.40  
  Purchase #5 $242.88   12.800%   $273.9686   $273.97   $273.95   $274.00  
  Purchase #6 $221.57   12.246%   $248.7035   $248.70   $248.70   $248.70  
  Purchase #7 $43.92   9.379%   $48.0393   $48.04   $48.05   $48.00  
  7 purchase totals = $978.17       $1,084.8085   $1,084.81   $1,084.80   $1,084.80