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 $40.71   13.432%   $46.1782   $46.18   $46.20   $46.20  
  Purchase #2 $93.85   13.164%   $106.2044   $106.20   $106.20   $106.20  
  Purchase #3 $83.60   12.311%   $93.892   $93.89   $93.90   $93.90  
  Purchase #4 $33.90   13.414%   $38.4473   $38.45   $38.45   $38.40  
  Purchase #5 $102.57   11.685%   $114.5553   $114.56   $114.55   $114.60  
  Purchase #6 $244.75   7.293%   $262.5996   $262.60   $262.60   $262.60  
  Purchase #7 $209.45   8.236%   $226.7003   $226.70   $226.70   $226.70  
  7 purchase totals = $808.83       $888.5771   $888.58   $888.60   $888.60