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 $197.61   8.298%   $214.0077   $214.01   $214.00   $214.00  
  Purchase #2 $37.41   13.167%   $42.3358   $42.34   $42.35   $42.30  
  Purchase #3 $113.87   6.652%   $121.4446   $121.44   $121.45   $121.40  
  Purchase #4 $180.86   5.479%   $190.7693   $190.77   $190.75   $190.80  
  Purchase #5 $11.37   7.655%   $12.2404   $12.24   $12.25   $12.20  
  Purchase #6 $183.79   12.686%   $207.1056   $207.11   $207.10   $207.10  
  Purchase #7 $53.59   8.573%   $58.1843   $58.18   $58.20   $58.20  
  7 purchase totals = $778.50       $846.0877   $846.09   $846.10   $846.00