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 $55.33   11.710%   $61.8091   $61.81   $61.80   $61.80  
  Purchase #2 $87.55   10.729%   $96.9432   $96.94   $96.95   $96.90  
  Purchase #3 $90.35   4.729%   $94.6227   $94.62   $94.60   $94.60  
  Purchase #4 $103.66   10.699%   $114.7506   $114.75   $114.75   $114.80  
  Purchase #5 $205.48   12.626%   $231.4239   $231.42   $231.40   $231.40  
  Purchase #6 $213.41   12.859%   $240.8524   $240.85   $240.85   $240.90  
  Purchase #7 $115.85   8.832%   $126.0819   $126.08   $126.10   $126.10  
  7 purchase totals = $871.63       $966.4838   $966.47   $966.45   $966.50