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 $242.93   3.461%   $251.3378   $251.34   $251.35   $251.30  
  Purchase #2 $39.35   7.488%   $42.2965   $42.30   $42.30   $42.30  
  Purchase #3 $159.60   10.127%   $175.7627   $175.76   $175.75   $175.80  
  Purchase #4 $103.65   10.281%   $114.3063   $114.31   $114.30   $114.30  
  Purchase #5 $23.51   8.292%   $25.4594   $25.46   $25.45   $25.50  
  Purchase #6 $180.87   12.703%   $203.8459   $203.85   $203.85   $203.80  
  Purchase #7 $79.68   3.573%   $82.527   $82.53   $82.55   $82.50  
  7 purchase totals = $829.59       $895.5356   $895.55   $895.55   $895.50