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 $165.63   10.761%   $183.4534   $183.45   $183.45   $183.50  
  Purchase #2 $29.91   12.387%   $33.615   $33.62   $33.60   $33.60  
  Purchase #3 $39.34   5.795%   $41.6198   $41.62   $41.60   $41.60  
  Purchase #4 $90.85   3.379%   $93.9198   $93.92   $93.90   $93.90  
  Purchase #5 $124.57   9.437%   $136.3257   $136.33   $136.35   $136.30  
  Purchase #6 $101.89   12.688%   $114.8178   $114.82   $114.80   $114.80  
  Purchase #7 $208.35   4.437%   $217.5945   $217.59   $217.60   $217.60  
  7 purchase totals = $760.54       $821.3460   $821.35   $821.30   $821.30