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 $52.31   7.356%   $56.1579   $56.16   $56.15   $56.20  
  Purchase #2 $242.68   10.355%   $267.8095   $267.81   $267.80   $267.80  
  Purchase #3 $221.31   12.636%   $249.2747   $249.27   $249.25   $249.30  
  Purchase #4 $51.67   3.414%   $53.434   $53.43   $53.45   $53.40  
  Purchase #5 $36.82   5.746%   $38.9357   $38.94   $38.95   $38.90  
  Purchase #6 $164.67   12.347%   $185.0018   $185.00   $185.00   $185.00  
  Purchase #7 $14.32   13.416%   $16.2412   $16.24   $16.25   $16.20  
  7 purchase totals = $783.78       $866.8548   $866.85   $866.85   $866.80