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 $77.48   11.152%   $86.1206   $86.12   $86.10   $86.10  
  Purchase #2 $8.77   10.549%   $9.6951   $9.70   $9.70   $9.70  
  Purchase #3 $193.90   3.495%   $200.6768   $200.68   $200.70   $200.70  
  Purchase #4 $59.57   4.351%   $62.1619   $62.16   $62.15   $62.20  
  Purchase #5 $215.78   12.643%   $243.0611   $243.06   $243.05   $243.10  
  Purchase #6 $103.36   13.783%   $117.6061   $117.61   $117.60   $117.60  
  Purchase #7 $166.53   6.102%   $176.6917   $176.69   $176.70   $176.70  
  7 purchase totals = $825.39       $896.0133   $896.02   $896.00   $896.10