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 $113.63   10.108%   $125.1157   $125.12   $125.10   $125.10  
  Purchase #2 $142.65   6.343%   $151.6983   $151.70   $151.70   $151.70  
  Purchase #3 $131.71   12.712%   $148.453   $148.45   $148.45   $148.50  
  Purchase #4 $131.28   11.541%   $146.431   $146.43   $146.45   $146.40  
  Purchase #5 $5.70   10.515%   $6.2994   $6.30   $6.30   $6.30  
  Purchase #6 $124.51   4.540%   $130.1628   $130.16   $130.15   $130.20  
  Purchase #7 $147.54   3.117%   $152.1388   $152.14   $152.15   $152.10  
  7 purchase totals = $797.02       $860.2990   $860.30   $860.30   $860.30