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 $208.91   12.611%   $235.2556   $235.26   $235.25   $235.30  
  Purchase #2 $152.54   11.797%   $170.5351   $170.54   $170.55   $170.50  
  Purchase #3 $188.70   12.811%   $212.8744   $212.87   $212.85   $212.90  
  Purchase #4 $236.39   3.462%   $244.5738   $244.57   $244.55   $244.60  
  Purchase #5 $42.39   7.676%   $45.6439   $45.64   $45.65   $45.60  
  Purchase #6 $38.76   8.373%   $42.0054   $42.01   $42.00   $42.00  
  Purchase #7 $172.81   12.660%   $194.6877   $194.69   $194.70   $194.70  
  7 purchase totals = $1,040.50       $1,145.5759   $1,145.58   $1,145.55   $1,145.60