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 $24.95   3.708%   $25.8751   $25.88   $25.90   $25.90  
  Purchase #2 $145.47   4.833%   $152.5006   $152.50   $152.50   $152.50  
  Purchase #3 $105.75   10.537%   $116.8929   $116.89   $116.90   $116.90  
  Purchase #4 $207.93   6.527%   $221.5016   $221.50   $221.50   $221.50  
  Purchase #5 $118.28   9.404%   $129.4031   $129.40   $129.40   $129.40  
  Purchase #6 $114.82   6.478%   $122.258   $122.26   $122.25   $122.30  
  Purchase #7 $241.35   4.102%   $251.2502   $251.25   $251.25   $251.30  
  7 purchase totals = $958.55       $1,019.6815   $1,019.68   $1,019.70   $1,019.80