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 $72.79   13.417%   $82.5562   $82.56   $82.55   $82.60  
  Purchase #2 $56.92   3.581%   $58.9583   $58.96   $58.95   $59.00  
  Purchase #3 $239.50   5.225%   $252.0139   $252.01   $252.00   $252.00  
  Purchase #4 $164.27   11.287%   $182.8112   $182.81   $182.80   $182.80  
  Purchase #5 $133.54   13.261%   $151.2487   $151.25   $151.25   $151.20  
  Purchase #6 $125.38   6.417%   $133.4256   $133.43   $133.45   $133.40  
  Purchase #7 $78.49   7.116%   $84.0753   $84.08   $84.10   $84.10  
  7 purchase totals = $870.89       $945.0892   $945.10   $945.10   $945.10