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 $49.71   5.853%   $52.6195   $52.62   $52.60   $52.60  
  Purchase #2 $75.96   7.473%   $81.6365   $81.64   $81.65   $81.60  
  Purchase #3 $107.42   5.410%   $113.2314   $113.23   $113.25   $113.20  
  Purchase #4 $132.35   8.155%   $143.1431   $143.14   $143.15   $143.10  
  Purchase #5 $41.58   11.686%   $46.439   $46.44   $46.45   $46.40  
  Purchase #6 $153.39   13.150%   $173.5608   $173.56   $173.55   $173.60  
  Purchase #7 $105.55   8.420%   $114.4373   $114.44   $114.45   $114.40  
  7 purchase totals = $665.96       $725.0676   $725.07   $725.10   $724.90