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 $22.96   5.604%   $24.2467   $24.25   $24.25   $24.20  
  Purchase #2 $194.64   4.241%   $202.8947   $202.89   $202.90   $202.90  
  Purchase #3 $13.76   8.683%   $14.9548   $14.95   $14.95   $15.00  
  Purchase #4 $157.88   6.443%   $168.0522   $168.05   $168.05   $168.10  
  Purchase #5 $11.40   12.693%   $12.847   $12.85   $12.85   $12.80  
  Purchase #6 $76.82   13.356%   $87.0801   $87.08   $87.10   $87.10  
  Purchase #7 $247.72   5.413%   $261.1291   $261.13   $261.15   $261.10  
  7 purchase totals = $725.18       $771.2046   $771.20   $771.25   $771.20