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 $242.56   4.845%   $254.312   $254.31   $254.30   $254.30  
  Purchase #2 $77.94   8.214%   $84.342   $84.34   $84.35   $84.30  
  Purchase #3 $157.77   10.610%   $174.5094   $174.51   $174.50   $174.50  
  Purchase #4 $236.27   9.623%   $259.0063   $259.01   $259.00   $259.00  
  Purchase #5 $180.68   13.652%   $205.3464   $205.35   $205.35   $205.30  
  Purchase #6 $241.66   10.394%   $266.7781   $266.78   $266.80   $266.80  
  Purchase #7 $103.64   6.806%   $110.6937   $110.69   $110.70   $110.70  
  7 purchase totals = $1,240.52       $1,354.9879   $1,354.99   $1,355.00   $1,354.90