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 $166.25   11.633%   $185.5899   $185.59   $185.60   $185.60  
  Purchase #2 $30.62   13.276%   $34.6851   $34.69   $34.70   $34.70  
  Purchase #3 $20.32   12.629%   $22.8862   $22.89   $22.90   $22.90  
  Purchase #4 $30.76   6.172%   $32.6585   $32.66   $32.65   $32.70  
  Purchase #5 $65.28   7.648%   $70.2726   $70.27   $70.25   $70.30  
  Purchase #6 $213.79   5.570%   $225.6981   $225.70   $225.70   $225.70  
  Purchase #7 $208.64   10.591%   $230.7371   $230.74   $230.75   $230.70  
  7 purchase totals = $735.66       $802.5275   $802.54   $802.55   $802.60