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 $108.71   12.524%   $122.3248   $122.32   $122.30   $122.30  
  Purchase #2 $70.71   6.486%   $75.2963   $75.30   $75.30   $75.30  
  Purchase #3 $57.78   10.421%   $63.8013   $63.80   $63.80   $63.80  
  Purchase #4 $102.63   13.764%   $116.756   $116.76   $116.75   $116.80  
  Purchase #5 $228.86   11.724%   $255.6915   $255.69   $255.70   $255.70  
  Purchase #6 $219.66   11.247%   $244.3652   $244.37   $244.35   $244.40  
  Purchase #7 $130.70   13.810%   $148.7497   $148.75   $148.75   $148.70  
  7 purchase totals = $919.05       $1,026.9848   $1,026.99   $1,026.95   $1,027.00