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 $73.95   5.132%   $77.7451   $77.75   $77.75   $77.70  
  Purchase #2 $124.81   13.411%   $141.5483   $141.55   $141.55   $141.50  
  Purchase #3 $30.48   7.195%   $32.673   $32.67   $32.65   $32.70  
  Purchase #4 $49.41   10.750%   $54.7216   $54.72   $54.70   $54.70  
  Purchase #5 $248.29   12.179%   $278.5292   $278.53   $278.55   $278.50  
  Purchase #6 $92.88   9.133%   $101.3627   $101.36   $101.35   $101.40  
  Purchase #7 $125.72   9.510%   $137.676   $137.68   $137.70   $137.70  
  7 purchase totals = $745.54       $824.2559   $824.26   $824.25   $824.20