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 $193.83   3.321%   $200.2671   $200.27   $200.25   $200.30  
  Purchase #2 $42.78   8.436%   $46.3889   $46.39   $46.40   $46.40  
  Purchase #3 $245.27   11.621%   $273.7728   $273.77   $273.75   $273.80  
  Purchase #4 $160.76   12.463%   $180.7955   $180.80   $180.80   $180.80  
  Purchase #5 $227.43   12.119%   $254.9922   $254.99   $255.00   $255.00  
  Purchase #6 $201.38   5.835%   $213.1305   $213.13   $213.15   $213.10  
  Purchase #7 $178.92   6.771%   $191.0347   $191.03   $191.05   $191.00  
  7 purchase totals = $1,250.37       $1,360.3817   $1,360.38   $1,360.40   $1,360.40