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 $205.81   6.776%   $219.7557   $219.76   $219.75   $219.80  
  Purchase #2 $93.77   3.775%   $97.3098   $97.31   $97.30   $97.30  
  Purchase #3 $46.62   7.260%   $50.0046   $50.00   $50.00   $50.00  
  Purchase #4 $178.93   8.358%   $193.885   $193.89   $193.90   $193.90  
  Purchase #5 $163.56   5.775%   $173.0056   $173.01   $173.00   $173.00  
  Purchase #6 $212.60   3.581%   $220.2132   $220.21   $220.20   $220.20  
  Purchase #7 $108.75   8.756%   $118.2722   $118.27   $118.25   $118.30  
  7 purchase totals = $1,010.04       $1,072.4461   $1,072.45   $1,072.40   $1,072.50