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 $82.25   12.685%   $92.6834   $92.68   $92.70   $92.70  
  Purchase #2 $226.41   5.742%   $239.4105   $239.41   $239.40   $239.40  
  Purchase #3 $237.83   4.671%   $248.939   $248.94   $248.95   $248.90  
  Purchase #4 $125.96   10.213%   $138.8243   $138.82   $138.80   $138.80  
  Purchase #5 $76.93   10.610%   $85.0923   $85.09   $85.10   $85.10  
  Purchase #6 $205.69   9.210%   $224.634   $224.63   $224.65   $224.60  
  Purchase #7 $89.92   4.241%   $93.7335   $93.73   $93.75   $93.70  
  7 purchase totals = $1,044.99       $1,123.3170   $1,123.30   $1,123.35   $1,123.20