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 $22.45   5.679%   $23.7249   $23.72   $23.70   $23.70  
  Purchase #2 $163.77   12.444%   $184.1495   $184.15   $184.15   $184.10  
  Purchase #3 $241.96   10.560%   $267.511   $267.51   $267.50   $267.50  
  Purchase #4 $153.40   12.782%   $173.0076   $173.01   $173.00   $173.00  
  Purchase #5 $53.43   13.161%   $60.4619   $60.46   $60.45   $60.50  
  Purchase #6 $94.99   7.659%   $102.2653   $102.27   $102.25   $102.30  
  Purchase #7 $240.91   6.472%   $256.5017   $256.50   $256.50   $256.50  
  7 purchase totals = $970.91       $1,067.6219   $1,067.62   $1,067.55   $1,067.60