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 $190.35   7.657%   $204.9251   $204.93   $204.95   $204.90  
  Purchase #2 $249.93   7.250%   $268.0499   $268.05   $268.05   $268.00  
  Purchase #3 $172.99   5.174%   $181.9405   $181.94   $181.95   $181.90  
  Purchase #4 $241.72   8.296%   $261.7731   $261.77   $261.75   $261.80  
  Purchase #5 $93.42   5.489%   $98.5478   $98.55   $98.55   $98.50  
  Purchase #6 $230.29   8.142%   $249.0402   $249.04   $249.05   $249.00  
  Purchase #7 $98.44   5.292%   $103.6494   $103.65   $103.65   $103.60  
  7 purchase totals = $1,277.14       $1,367.9260   $1,367.93   $1,367.95   $1,367.70