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 $241.83   11.610%   $269.9065   $269.91   $269.90   $269.90  
  Purchase #2 $187.46   7.652%   $201.8044   $201.80   $201.80   $201.80  
  Purchase #3 $127.37   12.823%   $143.7027   $143.70   $143.70   $143.70  
  Purchase #4 $9.98   3.595%   $10.3388   $10.34   $10.35   $10.30  
  Purchase #5 $9.99   8.262%   $10.8154   $10.82   $10.80   $10.80  
  Purchase #6 $69.85   8.607%   $75.862   $75.86   $75.85   $75.90  
  Purchase #7 $29.72   5.248%   $31.2797   $31.28   $31.30   $31.30  
  7 purchase totals = $676.20       $743.7095   $743.71   $743.70   $743.70