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 $132.70   8.470%   $143.9397   $143.94   $143.95   $143.90  
  Purchase #2 $247.56   11.231%   $275.3635   $275.36   $275.35   $275.40  
  Purchase #3 $43.43   9.813%   $47.6918   $47.69   $47.70   $47.70  
  Purchase #4 $189.94   9.407%   $207.8077   $207.81   $207.80   $207.80  
  Purchase #5 $31.69   10.736%   $35.0922   $35.09   $35.10   $35.10  
  Purchase #6 $208.37   13.600%   $236.7083   $236.71   $236.70   $236.70  
  Purchase #7 $65.66   13.246%   $74.3573   $74.36   $74.35   $74.40  
  7 purchase totals = $919.35       $1,020.9605   $1,020.96   $1,020.95   $1,021.00