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 $205.73   9.167%   $224.5893   $224.59   $224.60   $224.60  
  Purchase #2 $207.80   13.324%   $235.4873   $235.49   $235.50   $235.50  
  Purchase #3 $209.88   8.684%   $228.106   $228.11   $228.10   $228.10  
  Purchase #4 $72.67   3.650%   $75.3225   $75.32   $75.30   $75.30  
  Purchase #5 $225.66   11.775%   $252.2315   $252.23   $252.25   $252.20  
  Purchase #6 $192.53   10.127%   $212.0275   $212.03   $212.05   $212.00  
  Purchase #7 $41.43   10.567%   $45.8079   $45.81   $45.80   $45.80  
  7 purchase totals = $1,155.70       $1,273.5720   $1,273.58   $1,273.60   $1,273.50