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 $200.64   13.299%   $227.3231   $227.32   $227.30   $227.30  
  Purchase #2 $87.53   6.806%   $93.4873   $93.49   $93.50   $93.50  
  Purchase #3 $235.25   4.688%   $246.2785   $246.28   $246.30   $246.30  
  Purchase #4 $119.75   7.305%   $128.4977   $128.50   $128.50   $128.50  
  Purchase #5 $138.58   13.643%   $157.4865   $157.49   $157.50   $157.50  
  Purchase #6 $77.45   9.605%   $84.8891   $84.89   $84.90   $84.90  
  Purchase #7 $73.96   3.259%   $76.3704   $76.37   $76.35   $76.40  
  7 purchase totals = $933.16       $1,014.3326   $1,014.34   $1,014.35   $1,014.40