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 $213.45   13.349%   $241.9434   $241.94   $241.95   $241.90  
  Purchase #2 $54.94   7.186%   $58.888   $58.89   $58.90   $58.90  
  Purchase #3 $165.53   4.629%   $173.1924   $173.19   $173.20   $173.20  
  Purchase #4 $161.57   9.806%   $177.4136   $177.41   $177.40   $177.40  
  Purchase #5 $191.99   4.439%   $200.5124   $200.51   $200.50   $200.50  
  Purchase #6 $250.79   10.401%   $276.8747   $276.87   $276.85   $276.90  
  Purchase #7 $110.80   5.110%   $116.4619   $116.46   $116.45   $116.50  
  7 purchase totals = $1,149.07       $1,245.2864   $1,245.27   $1,245.25   $1,245.30