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 $181.59   13.549%   $206.1936   $206.19   $206.20   $206.20  
  Purchase #2 $54.60   8.167%   $59.0592   $59.06   $59.05   $59.10  
  Purchase #3 $65.61   3.217%   $67.7207   $67.72   $67.70   $67.70  
  Purchase #4 $145.70   8.648%   $158.3001   $158.30   $158.30   $158.30  
  Purchase #5 $164.29   6.334%   $174.6961   $174.70   $174.70   $174.70  
  Purchase #6 $69.75   9.210%   $76.174   $76.17   $76.15   $76.20  
  Purchase #7 $128.54   3.680%   $133.2703   $133.27   $133.25   $133.30  
  7 purchase totals = $810.08       $875.4140   $875.41   $875.35   $875.50