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 $111.63   10.156%   $122.9671   $122.97   $122.95   $123.00  
  Purchase #2 $114.46   4.333%   $119.4196   $119.42   $119.40   $119.40  
  Purchase #3 $52.97   13.609%   $60.1787   $60.18   $60.20   $60.20  
  Purchase #4 $179.70   5.148%   $188.951   $188.95   $188.95   $189.00  
  Purchase #5 $173.49   11.482%   $193.4101   $193.41   $193.40   $193.40  
  Purchase #6 $120.94   3.725%   $125.445   $125.45   $125.45   $125.40  
  Purchase #7 $49.36   13.435%   $55.9915   $55.99   $56.00   $56.00  
  7 purchase totals = $802.55       $866.3630   $866.37   $866.35   $866.40