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 $32.42   13.326%   $36.7403   $36.74   $36.75   $36.70  
  Purchase #2 $40.78   13.754%   $46.3889   $46.39   $46.40   $46.40  
  Purchase #3 $11.95   4.159%   $12.447   $12.45   $12.45   $12.40  
  Purchase #4 $169.49   3.787%   $175.9086   $175.91   $175.90   $175.90  
  Purchase #5 $40.66   3.531%   $42.0957   $42.10   $42.10   $42.10  
  Purchase #6 $219.67   7.153%   $235.383   $235.38   $235.40   $235.40  
  Purchase #7 $192.94   7.544%   $207.4954   $207.50   $207.50   $207.50  
  7 purchase totals = $707.91       $756.4589   $756.47   $756.50   $756.40