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 $243.74   13.506%   $276.6595   $276.66   $276.65   $276.70  
  Purchase #2 $127.54   5.378%   $134.3991   $134.40   $134.40   $134.40  
  Purchase #3 $197.70   4.518%   $206.6321   $206.63   $206.65   $206.60  
  Purchase #4 $85.94   13.430%   $97.4817   $97.48   $97.50   $97.50  
  Purchase #5 $205.90   12.497%   $231.6313   $231.63   $231.65   $231.60  
  Purchase #6 $49.63   9.624%   $54.4064   $54.41   $54.40   $54.40  
  Purchase #7 $158.77   9.391%   $173.6801   $173.68   $173.70   $173.70  
  7 purchase totals = $1,069.22       $1,174.8902   $1,174.89   $1,174.95   $1,174.90