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 $45.99   13.467%   $52.1835   $52.18   $52.20   $52.20  
  Purchase #2 $50.94   4.278%   $53.1192   $53.12   $53.10   $53.10  
  Purchase #3 $194.80   6.475%   $207.4133   $207.41   $207.40   $207.40  
  Purchase #4 $245.72   6.431%   $261.5223   $261.52   $261.50   $261.50  
  Purchase #5 $105.97   7.581%   $114.0036   $114.00   $114.00   $114.00  
  Purchase #6 $115.71   13.446%   $131.2684   $131.27   $131.25   $131.30  
  Purchase #7 $9.93   10.800%   $11.0024   $11.00   $11.00   $11.00  
  7 purchase totals = $769.06       $830.5127   $830.50   $830.45   $830.50