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 $51.43   11.660%   $57.4267   $57.43   $57.45   $57.40  
  Purchase #2 $22.35   6.727%   $23.8535   $23.85   $23.85   $23.90  
  Purchase #3 $175.76   8.733%   $191.1091   $191.11   $191.10   $191.10  
  Purchase #4 $196.54   13.191%   $222.4656   $222.47   $222.45   $222.50  
  Purchase #5 $217.95   5.521%   $229.983   $229.98   $230.00   $230.00  
  Purchase #6 $231.87   9.718%   $254.4031   $254.40   $254.40   $254.40  
  Purchase #7 $41.38   8.586%   $44.9329   $44.93   $44.95   $44.90  
  7 purchase totals = $937.28       $1,024.1739   $1,024.17   $1,024.20   $1,024.20