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 $24.54   6.651%   $26.1722   $26.17   $26.15   $26.20  
  Purchase #2 $69.87   6.872%   $74.6715   $74.67   $74.65   $74.70  
  Purchase #3 $197.50   4.759%   $206.899   $206.90   $206.90   $206.90  
  Purchase #4 $184.72   3.733%   $191.6156   $191.62   $191.60   $191.60  
  Purchase #5 $28.95   4.426%   $30.2313   $30.23   $30.25   $30.20  
  Purchase #6 $244.68   9.317%   $267.4768   $267.48   $267.50   $267.50  
  Purchase #7 $221.41   7.123%   $237.181   $237.18   $237.20   $237.20  
  7 purchase totals = $971.67       $1,034.2474   $1,034.25   $1,034.25   $1,034.30