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 $100.72   4.503%   $105.2554   $105.26   $105.25   $105.30  
  Purchase #2 $165.46   13.506%   $187.807   $187.81   $187.80   $187.80  
  Purchase #3 $51.77   5.115%   $54.418   $54.42   $54.40   $54.40  
  Purchase #4 $114.91   12.376%   $129.1313   $129.13   $129.15   $129.10  
  Purchase #5 $32.88   7.645%   $35.3937   $35.39   $35.40   $35.40  
  Purchase #6 $19.63   12.669%   $22.1169   $22.12   $22.10   $22.10  
  Purchase #7 $23.59   4.640%   $24.6846   $24.68   $24.70   $24.70  
  7 purchase totals = $508.96       $558.8069   $558.81   $558.80   $558.80