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 $54.76   5.324%   $57.6754   $57.68   $57.70   $57.70  
  Purchase #2 $30.26   10.532%   $33.447   $33.45   $33.45   $33.40  
  Purchase #3 $76.51   12.790%   $86.2956   $86.30   $86.30   $86.30  
  Purchase #4 $213.39   10.775%   $236.3828   $236.38   $236.40   $236.40  
  Purchase #5 $38.31   6.399%   $40.7615   $40.76   $40.75   $40.80  
  Purchase #6 $115.70   8.402%   $125.4211   $125.42   $125.40   $125.40  
  Purchase #7 $238.35   5.176%   $250.687   $250.69   $250.70   $250.70  
  7 purchase totals = $767.28       $830.6704   $830.68   $830.70   $830.70