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 $119.87   3.233%   $123.7454   $123.75   $123.75   $123.70  
  Purchase #2 $144.77   11.161%   $160.9278   $160.93   $160.95   $160.90  
  Purchase #3 $164.83   8.251%   $178.4301   $178.43   $178.45   $178.40  
  Purchase #4 $33.32   4.679%   $34.879   $34.88   $34.90   $34.90  
  Purchase #5 $22.95   4.393%   $23.9582   $23.96   $23.95   $24.00  
  Purchase #6 $150.50   6.526%   $160.3216   $160.32   $160.30   $160.30  
  Purchase #7 $98.99   10.781%   $109.6621   $109.66   $109.65   $109.70  
  7 purchase totals = $735.23       $791.9242   $791.93   $791.95   $791.90