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 $113.51   13.796%   $129.1698   $129.17   $129.15   $129.20  
  Purchase #2 $204.47   6.245%   $217.2392   $217.24   $217.25   $217.20  
  Purchase #3 $113.89   9.481%   $124.6879   $124.69   $124.70   $124.70  
  Purchase #4 $154.46   13.426%   $175.1978   $175.20   $175.20   $175.20  
  Purchase #5 $47.72   6.360%   $50.755   $50.76   $50.75   $50.80  
  Purchase #6 $248.48   13.188%   $281.2495   $281.25   $281.25   $281.20  
  Purchase #7 $41.69   8.721%   $45.3258   $45.33   $45.35   $45.30  
  7 purchase totals = $924.22       $1,023.6250   $1,023.64   $1,023.65   $1,023.60