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 $71.88   11.635%   $80.2432   $80.24   $80.25   $80.20  
  Purchase #2 $62.69   3.302%   $64.76   $64.76   $64.75   $64.80  
  Purchase #3 $52.81   11.813%   $59.0484   $59.05   $59.05   $59.00  
  Purchase #4 $161.99   12.691%   $182.5482   $182.55   $182.55   $182.50  
  Purchase #5 $81.77   6.465%   $87.0564   $87.06   $87.05   $87.10  
  Purchase #6 $248.31   11.547%   $276.9824   $276.98   $277.00   $277.00  
  Purchase #7 $69.26   8.697%   $75.2835   $75.28   $75.30   $75.30  
  7 purchase totals = $748.71       $825.9221   $825.92   $825.95   $825.90