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 $144.47   12.554%   $162.6068   $162.61   $162.60   $162.60  
  Purchase #2 $188.25   9.613%   $206.3465   $206.35   $206.35   $206.30  
  Purchase #3 $67.66   11.373%   $75.355   $75.36   $75.35   $75.40  
  Purchase #4 $166.65   4.258%   $173.746   $173.75   $173.75   $173.70  
  Purchase #5 $195.73   6.104%   $207.6774   $207.68   $207.70   $207.70  
  Purchase #6 $163.52   12.577%   $184.0859   $184.09   $184.10   $184.10  
  Purchase #7 $59.68   5.431%   $62.9212   $62.92   $62.90   $62.90  
  7 purchase totals = $985.96       $1,072.7388   $1,072.76   $1,072.75   $1,072.70