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 $140.26   11.731%   $156.7139   $156.71   $156.70   $156.70  
  Purchase #2 $74.26   7.664%   $79.9513   $79.95   $79.95   $80.00  
  Purchase #3 $187.47   3.192%   $193.454   $193.45   $193.45   $193.50  
  Purchase #4 $32.79   8.141%   $35.4594   $35.46   $35.45   $35.50  
  Purchase #5 $49.54   6.434%   $52.7274   $52.73   $52.75   $52.70  
  Purchase #6 $246.30   3.437%   $254.7653   $254.77   $254.75   $254.80  
  Purchase #7 $110.36   11.207%   $122.728   $122.73   $122.75   $122.70  
  7 purchase totals = $840.98       $895.7993   $895.80   $895.80   $895.90