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 $236.52   8.319%   $256.1961   $256.20   $256.20   $256.20  
  Purchase #2 $23.46   10.773%   $25.9873   $25.99   $26.00   $26.00  
  Purchase #3 $45.44   12.640%   $51.1836   $51.18   $51.20   $51.20  
  Purchase #4 $115.36   8.316%   $124.9533   $124.95   $124.95   $125.00  
  Purchase #5 $119.81   11.673%   $133.7954   $133.80   $133.80   $133.80  
  Purchase #6 $53.34   6.857%   $56.9975   $57.00   $57.00   $57.00  
  Purchase #7 $160.79   7.766%   $173.277   $173.28   $173.30   $173.30  
  7 purchase totals = $754.72       $822.3902   $822.40   $822.45   $822.50