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 $90.48   3.792%   $93.911   $93.91   $93.90   $93.90  
  Purchase #2 $11.63   12.194%   $13.0482   $13.05   $13.05   $13.00  
  Purchase #3 $95.41   10.312%   $105.2487   $105.25   $105.25   $105.20  
  Purchase #4 $199.61   3.380%   $206.3568   $206.36   $206.35   $206.40  
  Purchase #5 $69.48   6.418%   $73.9392   $73.94   $73.95   $73.90  
  Purchase #6 $160.90   3.788%   $166.9949   $166.99   $167.00   $167.00  
  Purchase #7 $239.85   3.233%   $247.6044   $247.60   $247.60   $247.60  
  7 purchase totals = $867.36       $907.1032   $907.10   $907.10   $907.00