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 $189.92   5.859%   $201.0474   $201.05   $201.05   $201.00  
  Purchase #2 $201.32   5.542%   $212.4772   $212.48   $212.50   $212.50  
  Purchase #3 $33.72   6.393%   $35.8757   $35.88   $35.90   $35.90  
  Purchase #4 $230.29   8.500%   $249.8647   $249.86   $249.85   $249.90  
  Purchase #5 $119.49   8.777%   $129.9776   $129.98   $130.00   $130.00  
  Purchase #6 $54.41   4.105%   $56.6435   $56.64   $56.65   $56.60  
  Purchase #7 $63.41   4.557%   $66.2996   $66.30   $66.30   $66.30  
  7 purchase totals = $892.56       $952.1857   $952.19   $952.25   $952.20