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 $120.68   5.383%   $127.1762   $127.18   $127.20   $127.20  
  Purchase #2 $91.94   11.194%   $102.2318   $102.23   $102.25   $102.20  
  Purchase #3 $24.34   12.584%   $27.4029   $27.40   $27.40   $27.40  
  Purchase #4 $155.91   8.240%   $168.757   $168.76   $168.75   $168.80  
  Purchase #5 $43.31   12.692%   $48.8069   $48.81   $48.80   $48.80  
  Purchase #6 $114.58   9.702%   $125.6966   $125.70   $125.70   $125.70  
  Purchase #7 $231.25   13.234%   $261.8536   $261.85   $261.85   $261.90  
  7 purchase totals = $782.01       $861.9250   $861.93   $861.95   $862.00