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 $248.28   6.716%   $264.9545   $264.95   $264.95   $265.00  
  Purchase #2 $221.99   4.839%   $232.7321   $232.73   $232.75   $232.70  
  Purchase #3 $26.30   8.503%   $28.5363   $28.54   $28.55   $28.50  
  Purchase #4 $80.81   10.684%   $89.4437   $89.44   $89.45   $89.40  
  Purchase #5 $164.97   5.831%   $174.5894   $174.59   $174.60   $174.60  
  Purchase #6 $108.91   11.428%   $121.3562   $121.36   $121.35   $121.40  
  Purchase #7 $21.83   3.823%   $22.6646   $22.66   $22.65   $22.70  
  7 purchase totals = $873.09       $934.2768   $934.27   $934.30   $934.30