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 $208.46   13.854%   $237.34   $237.34   $237.35   $237.30  
  Purchase #2 $38.90   5.329%   $40.973   $40.97   $40.95   $41.00  
  Purchase #3 $86.64   4.717%   $90.7268   $90.73   $90.75   $90.70  
  Purchase #4 $103.39   3.494%   $107.0024   $107.00   $107.00   $107.00  
  Purchase #5 $237.64   11.420%   $264.7785   $264.78   $264.80   $264.80  
  Purchase #6 $171.40   11.713%   $191.4761   $191.48   $191.50   $191.50  
  Purchase #7 $88.63   8.674%   $96.3178   $96.32   $96.30   $96.30  
  7 purchase totals = $935.06       $1,028.6146   $1,028.62   $1,028.65   $1,028.60