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 $237.29   5.467%   $250.2626   $250.26   $250.25   $250.30  
  Purchase #2 $87.33   7.284%   $93.6911   $93.69   $93.70   $93.70  
  Purchase #3 $53.90   8.215%   $58.3279   $58.33   $58.35   $58.30  
  Purchase #4 $43.29   12.179%   $48.5623   $48.56   $48.55   $48.60  
  Purchase #5 $175.39   12.428%   $197.1875   $197.19   $197.20   $197.20  
  Purchase #6 $245.88   5.448%   $259.2755   $259.28   $259.30   $259.30  
  Purchase #7 $203.67   4.839%   $213.5256   $213.53   $213.55   $213.50  
  7 purchase totals = $1,046.75       $1,120.8325   $1,120.84   $1,120.90   $1,120.90