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 $147.49   10.581%   $163.0959   $163.10   $163.10   $163.10  
  Purchase #2 $141.69   10.597%   $156.7049   $156.70   $156.70   $156.70  
  Purchase #3 $91.97   5.735%   $97.2445   $97.24   $97.25   $97.20  
  Purchase #4 $143.79   9.719%   $157.765   $157.77   $157.75   $157.80  
  Purchase #5 $163.49   10.206%   $180.1758   $180.18   $180.20   $180.20  
  Purchase #6 $51.37   9.289%   $56.1418   $56.14   $56.15   $56.10  
  Purchase #7 $68.61   3.284%   $70.8632   $70.86   $70.85   $70.90  
  7 purchase totals = $808.41       $881.9911   $881.99   $882.00   $882.00