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 $230.90   13.485%   $262.0369   $262.04   $262.05   $262.00  
  Purchase #2 $204.45   7.727%   $220.2479   $220.25   $220.25   $220.20  
  Purchase #3 $157.75   11.756%   $176.2951   $176.30   $176.30   $176.30  
  Purchase #4 $156.94   10.504%   $173.425   $173.43   $173.45   $173.40  
  Purchase #5 $151.30   7.547%   $162.7186   $162.72   $162.70   $162.70  
  Purchase #6 $124.56   12.328%   $139.9158   $139.92   $139.90   $139.90  
  Purchase #7 $29.49   9.360%   $32.2503   $32.25   $32.25   $32.30  
  7 purchase totals = $1,055.39       $1,166.8896   $1,166.91   $1,166.90   $1,166.80