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 $176.66   11.277%   $196.5819   $196.58   $196.60   $196.60  
  Purchase #2 $23.37   3.588%   $24.2085   $24.21   $24.20   $24.20  
  Purchase #3 $118.91   5.174%   $125.0624   $125.06   $125.05   $125.10  
  Purchase #4 $61.39   13.263%   $69.5322   $69.53   $69.55   $69.50  
  Purchase #5 $184.81   7.531%   $198.728   $198.73   $198.75   $198.70  
  Purchase #6 $25.61   4.747%   $26.8257   $26.83   $26.85   $26.80  
  Purchase #7 $173.37   5.705%   $183.2608   $183.26   $183.25   $183.30  
  7 purchase totals = $764.12       $824.1995   $824.20   $824.25   $824.20