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 $183.41   8.259%   $198.5578   $198.56   $198.55   $198.60  
  Purchase #2 $223.89   5.364%   $235.8995   $235.90   $235.90   $235.90  
  Purchase #3 $78.97   5.788%   $83.5408   $83.54   $83.55   $83.50  
  Purchase #4 $126.40   8.585%   $137.2514   $137.25   $137.25   $137.30  
  Purchase #5 $105.49   9.606%   $115.6234   $115.62   $115.60   $115.60  
  Purchase #6 $245.63   11.802%   $274.6193   $274.62   $274.60   $274.60  
  Purchase #7 $62.35   9.772%   $68.4428   $68.44   $68.45   $68.40  
  7 purchase totals = $1,026.14       $1,113.9350   $1,113.93   $1,113.90   $1,113.90