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 $98.82   6.581%   $105.3233   $105.32   $105.30   $105.30  
  Purchase #2 $247.82   11.825%   $277.1247   $277.12   $277.10   $277.10  
  Purchase #3 $155.38   9.812%   $170.6259   $170.63   $170.65   $170.60  
  Purchase #4 $173.34   3.641%   $179.6513   $179.65   $179.65   $179.70  
  Purchase #5 $62.50   11.526%   $69.7038   $69.70   $69.70   $69.70  
  Purchase #6 $107.77   6.112%   $114.3569   $114.36   $114.35   $114.40  
  Purchase #7 $86.86   3.417%   $89.828   $89.83   $89.85   $89.80  
  7 purchase totals = $932.49       $1,006.6139   $1,006.61   $1,006.60   $1,006.60