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 $86.43   6.380%   $91.9442   $91.94   $91.95   $91.90  
  Purchase #2 $208.82   11.844%   $233.5526   $233.55   $233.55   $233.60  
  Purchase #3 $67.36   8.757%   $73.2587   $73.26   $73.25   $73.30  
  Purchase #4 $226.66   5.191%   $238.4259   $238.43   $238.45   $238.40  
  Purchase #5 $160.98   10.470%   $177.8346   $177.83   $177.85   $177.80  
  Purchase #6 $21.84   6.502%   $23.26   $23.26   $23.25   $23.30  
  Purchase #7 $179.82   3.433%   $185.9932   $185.99   $186.00   $186.00  
  7 purchase totals = $951.91       $1,024.2692   $1,024.26   $1,024.30   $1,024.30