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 $14.48   10.831%   $16.0483   $16.05   $16.05   $16.00  
  Purchase #2 $211.58   11.120%   $235.1077   $235.11   $235.10   $235.10  
  Purchase #3 $19.82   8.728%   $21.5499   $21.55   $21.55   $21.50  
  Purchase #4 $173.31   5.611%   $183.0344   $183.03   $183.05   $183.00  
  Purchase #5 $41.43   13.553%   $47.045   $47.05   $47.05   $47.00  
  Purchase #6 $244.35   6.860%   $261.1124   $261.11   $261.10   $261.10  
  Purchase #7 $33.57   11.433%   $37.4081   $37.41   $37.40   $37.40  
  7 purchase totals = $738.54       $801.3058   $801.31   $801.30   $801.10