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 $49.65   10.804%   $55.0142   $55.01   $55.00   $55.00  
  Purchase #2 $224.25   12.611%   $252.5302   $252.53   $252.55   $252.50  
  Purchase #3 $73.42   13.435%   $83.284   $83.28   $83.30   $83.30  
  Purchase #4 $222.38   6.704%   $237.2884   $237.29   $237.30   $237.30  
  Purchase #5 $24.84   12.153%   $27.8588   $27.86   $27.85   $27.90  
  Purchase #6 $238.76   4.241%   $248.8858   $248.89   $248.90   $248.90  
  Purchase #7 $189.39   4.778%   $198.4391   $198.44   $198.45   $198.40  
  7 purchase totals = $1,022.69       $1,103.3005   $1,103.30   $1,103.35   $1,103.30