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 $24.62   3.583%   $25.5021   $25.50   $25.50   $25.50  
  Purchase #2 $226.48   9.180%   $247.2709   $247.27   $247.25   $247.30  
  Purchase #3 $239.31   3.848%   $248.5186   $248.52   $248.50   $248.50  
  Purchase #4 $230.56   13.744%   $262.2482   $262.25   $262.25   $262.20  
  Purchase #5 $39.32   11.125%   $43.6944   $43.69   $43.70   $43.70  
  Purchase #6 $236.35   4.663%   $247.371   $247.37   $247.35   $247.40  
  Purchase #7 $249.26   5.418%   $262.7649   $262.76   $262.75   $262.80  
  7 purchase totals = $1,245.90       $1,337.3701   $1,337.36   $1,337.30   $1,337.40