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 $249.67   10.423%   $275.6931   $275.69   $275.70   $275.70  
  Purchase #2 $38.25   11.306%   $42.5745   $42.57   $42.55   $42.60  
  Purchase #3 $200.51   3.835%   $208.1996   $208.20   $208.20   $208.20  
  Purchase #4 $184.73   11.654%   $206.2584   $206.26   $206.25   $206.30  
  Purchase #5 $164.50   10.862%   $182.368   $182.37   $182.35   $182.40  
  Purchase #6 $161.66   6.744%   $172.5624   $172.56   $172.55   $172.60  
  Purchase #7 $111.35   4.438%   $116.2917   $116.29   $116.30   $116.30  
  7 purchase totals = $1,110.67       $1,203.9477   $1,203.94   $1,203.90   $1,204.10