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 $186.85   5.792%   $197.6724   $197.67   $197.65   $197.70  
  Purchase #2 $60.26   7.641%   $64.8645   $64.86   $64.85   $64.90  
  Purchase #3 $77.68   6.863%   $83.0112   $83.01   $83.00   $83.00  
  Purchase #4 $38.76   13.609%   $44.0348   $44.03   $44.05   $44.00  
  Purchase #5 $105.40   12.795%   $118.8859   $118.89   $118.90   $118.90  
  Purchase #6 $227.45   6.271%   $241.7134   $241.71   $241.70   $241.70  
  Purchase #7 $233.95   8.847%   $254.6476   $254.65   $254.65   $254.60  
  7 purchase totals = $930.35       $1,004.8298   $1,004.82   $1,004.80   $1,004.80