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 $243.25   12.514%   $273.6903   $273.69   $273.70   $273.70  
  Purchase #2 $180.53   9.348%   $197.4059   $197.41   $197.40   $197.40  
  Purchase #3 $152.46   7.392%   $163.7298   $163.73   $163.75   $163.70  
  Purchase #4 $127.48   3.194%   $131.5517   $131.55   $131.55   $131.60  
  Purchase #5 $118.81   13.387%   $134.7151   $134.72   $134.70   $134.70  
  Purchase #6 $149.89   5.232%   $157.7322   $157.73   $157.75   $157.70  
  Purchase #7 $62.93   4.486%   $65.753   $65.75   $65.75   $65.80  
  7 purchase totals = $1,035.35       $1,124.5780   $1,124.58   $1,124.60   $1,124.60