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 $245.94   3.603%   $254.8012   $254.80   $254.80   $254.80  
  Purchase #2 $208.35   4.363%   $217.4403   $217.44   $217.45   $217.40  
  Purchase #3 $246.41   5.262%   $259.3761   $259.38   $259.40   $259.40  
  Purchase #4 $228.25   11.308%   $254.0605   $254.06   $254.05   $254.10  
  Purchase #5 $106.93   6.266%   $113.6302   $113.63   $113.65   $113.60  
  Purchase #6 $30.78   8.132%   $33.283   $33.28   $33.30   $33.30  
  Purchase #7 $190.39   4.318%   $198.611   $198.61   $198.60   $198.60  
  7 purchase totals = $1,257.05       $1,331.2023   $1,331.20   $1,331.25   $1,331.20