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 $67.46   9.129%   $73.6184   $73.62   $73.60   $73.60  
  Purchase #2 $103.49   10.798%   $114.6649   $114.66   $114.65   $114.70  
  Purchase #3 $69.34   7.375%   $74.4538   $74.45   $74.45   $74.50  
  Purchase #4 $249.47   13.797%   $283.8894   $283.89   $283.90   $283.90  
  Purchase #5 $67.39   7.416%   $72.3876   $72.39   $72.40   $72.40  
  Purchase #6 $54.45   10.253%   $60.0328   $60.03   $60.05   $60.00  
  Purchase #7 $102.60   4.307%   $107.019   $107.02   $107.00   $107.00  
  7 purchase totals = $714.20       $786.0659   $786.06   $786.05   $786.10