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 $180.28   13.303%   $204.2626   $204.26   $204.25   $204.30  
  Purchase #2 $190.34   3.263%   $196.5508   $196.55   $196.55   $196.60  
  Purchase #3 $164.73   12.723%   $185.6886   $185.69   $185.70   $185.70  
  Purchase #4 $41.97   6.591%   $44.7362   $44.74   $44.75   $44.70  
  Purchase #5 $119.93   5.631%   $126.6833   $126.68   $126.70   $126.70  
  Purchase #6 $35.71   4.839%   $37.438   $37.44   $37.45   $37.40  
  Purchase #7 $244.27   8.148%   $264.1731   $264.17   $264.15   $264.20  
  7 purchase totals = $977.23       $1,059.5326   $1,059.53   $1,059.55   $1,059.60