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 $37.77   8.647%   $41.036   $41.04   $41.05   $41.00  
  Purchase #2 $38.42   13.723%   $43.6924   $43.69   $43.70   $43.70  
  Purchase #3 $63.76   9.717%   $69.9556   $69.96   $69.95   $70.00  
  Purchase #4 $198.25   4.725%   $207.6173   $207.62   $207.60   $207.60  
  Purchase #5 $209.47   7.463%   $225.1027   $225.10   $225.10   $225.10  
  Purchase #6 $114.54   5.318%   $120.6312   $120.63   $120.65   $120.60  
  Purchase #7 $246.44   5.694%   $260.4723   $260.47   $260.45   $260.50  
  7 purchase totals = $908.65       $968.5075   $968.51   $968.50   $968.50