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 $56.97   7.429%   $61.2023   $61.20   $61.20   $61.20  
  Purchase #2 $129.85   8.548%   $140.9496   $140.95   $140.95   $140.90  
  Purchase #3 $125.78   10.231%   $138.6486   $138.65   $138.65   $138.60  
  Purchase #4 $191.37   10.724%   $211.8925   $211.89   $211.90   $211.90  
  Purchase #5 $50.81   9.458%   $55.6156   $55.62   $55.60   $55.60  
  Purchase #6 $191.35   11.483%   $213.3227   $213.32   $213.30   $213.30  
  Purchase #7 $173.43   6.732%   $185.1053   $185.11   $185.10   $185.10  
  7 purchase totals = $919.56       $1,006.7366   $1,006.74   $1,006.70   $1,006.60