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 $134.37   5.112%   $141.239   $141.24   $141.25   $141.20  
  Purchase #2 $193.62   3.226%   $199.8662   $199.87   $199.85   $199.90  
  Purchase #3 $76.92   3.228%   $79.403   $79.40   $79.40   $79.40  
  Purchase #4 $109.48   4.665%   $114.5872   $114.59   $114.60   $114.60  
  Purchase #5 $241.66   7.282%   $259.2577   $259.26   $259.25   $259.30  
  Purchase #6 $107.51   13.797%   $122.3432   $122.34   $122.35   $122.30  
  Purchase #7 $98.73   11.503%   $110.0869   $110.09   $110.10   $110.10  
  7 purchase totals = $962.29       $1,026.7832   $1,026.79   $1,026.80   $1,026.80