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 $70.37   10.256%   $77.5871   $77.59   $77.60   $77.60  
  Purchase #2 $135.87   13.144%   $153.7288   $153.73   $153.75   $153.70  
  Purchase #3 $156.64   12.546%   $176.2921   $176.29   $176.30   $176.30  
  Purchase #4 $157.32   9.724%   $172.6178   $172.62   $172.60   $172.60  
  Purchase #5 $58.27   10.225%   $64.2281   $64.23   $64.25   $64.20  
  Purchase #6 $218.54   9.476%   $239.2489   $239.25   $239.25   $239.20  
  Purchase #7 $135.30   5.293%   $142.4614   $142.46   $142.45   $142.50  
  7 purchase totals = $932.31       $1,026.1642   $1,026.17   $1,026.20   $1,026.10