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 $59.86   13.573%   $67.9848   $67.98   $68.00   $68.00  
  Purchase #2 $48.30   13.256%   $54.7026   $54.70   $54.70   $54.70  
  Purchase #3 $110.66   7.808%   $119.3003   $119.30   $119.30   $119.30  
  Purchase #4 $117.25   4.436%   $122.4512   $122.45   $122.45   $122.50  
  Purchase #5 $223.35   10.698%   $247.244   $247.24   $247.25   $247.20  
  Purchase #6 $240.84   3.531%   $249.3441   $249.34   $249.35   $249.30  
  Purchase #7 $239.83   9.258%   $262.0335   $262.03   $262.05   $262.00  
  7 purchase totals = $1,040.09       $1,123.0605   $1,123.04   $1,123.10   $1,123.00