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 $224.39   9.563%   $245.8484   $245.85   $245.85   $245.80  
  Purchase #2 $119.68   3.140%   $123.438   $123.44   $123.45   $123.40  
  Purchase #3 $39.39   13.520%   $44.7155   $44.72   $44.70   $44.70  
  Purchase #4 $144.67   12.705%   $163.0503   $163.05   $163.05   $163.10  
  Purchase #5 $179.64   12.168%   $201.4986   $201.50   $201.50   $201.50  
  Purchase #6 $114.99   3.740%   $119.2906   $119.29   $119.30   $119.30  
  Purchase #7 $66.59   13.569%   $75.6256   $75.63   $75.65   $75.60  
  7 purchase totals = $889.35       $973.4670   $973.48   $973.50   $973.40