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 $23.82   9.790%   $26.152   $26.15   $26.15   $26.20  
  Purchase #2 $71.62   6.709%   $76.425   $76.43   $76.45   $76.40  
  Purchase #3 $88.82   3.358%   $91.8026   $91.80   $91.80   $91.80  
  Purchase #4 $59.75   13.608%   $67.8808   $67.88   $67.90   $67.90  
  Purchase #5 $196.91   3.301%   $203.41   $203.41   $203.40   $203.40  
  Purchase #6 $125.60   13.304%   $142.3098   $142.31   $142.30   $142.30  
  Purchase #7 $43.34   10.196%   $47.7589   $47.76   $47.75   $47.80  
  7 purchase totals = $609.86       $655.7391   $655.74   $655.75   $655.80