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 $48.92   11.690%   $54.6387   $54.64   $54.65   $54.60  
  Purchase #2 $104.54   9.424%   $114.3918   $114.39   $114.40   $114.40  
  Purchase #3 $164.70   10.869%   $182.6012   $182.60   $182.60   $182.60  
  Purchase #4 $108.26   13.270%   $122.6261   $122.63   $122.65   $122.60  
  Purchase #5 $75.54   4.204%   $78.7157   $78.72   $78.70   $78.70  
  Purchase #6 $241.77   3.280%   $249.7001   $249.70   $249.70   $249.70  
  Purchase #7 $19.64   13.674%   $22.3256   $22.33   $22.35   $22.30  
  7 purchase totals = $763.37       $824.9992   $825.01   $825.05   $824.90