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 $74.25   3.464%   $76.822   $76.82   $76.80   $76.80  
  Purchase #2 $44.29   6.757%   $47.2827   $47.28   $47.30   $47.30  
  Purchase #3 $60.36   12.482%   $67.8941   $67.89   $67.90   $67.90  
  Purchase #4 $148.92   4.203%   $155.1791   $155.18   $155.20   $155.20  
  Purchase #5 $179.69   10.566%   $198.676   $198.68   $198.70   $198.70  
  Purchase #6 $103.78   10.425%   $114.5991   $114.60   $114.60   $114.60  
  Purchase #7 $179.74   4.544%   $187.9074   $187.91   $187.90   $187.90  
  7 purchase totals = $791.03       $848.3604   $848.36   $848.40   $848.40