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 $118.87   4.874%   $124.6637   $124.66   $124.65   $124.70  
  Purchase #2 $138.80   9.310%   $151.7223   $151.72   $151.70   $151.70  
  Purchase #3 $230.75   7.859%   $248.8846   $248.88   $248.90   $248.90  
  Purchase #4 $19.28   6.227%   $20.4806   $20.48   $20.50   $20.50  
  Purchase #5 $71.62   13.730%   $81.4534   $81.45   $81.45   $81.50  
  Purchase #6 $173.87   13.154%   $196.7409   $196.74   $196.75   $196.70  
  Purchase #7 $204.38   9.770%   $224.3479   $224.35   $224.35   $224.30  
  7 purchase totals = $957.57       $1,048.2934   $1,048.28   $1,048.30   $1,048.30