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 $91.99   6.124%   $97.6235   $97.62   $97.60   $97.60  
  Purchase #2 $222.84   11.441%   $248.3351   $248.34   $248.35   $248.30  
  Purchase #3 $176.41   8.186%   $190.8509   $190.85   $190.85   $190.90  
  Purchase #4 $172.50   13.746%   $196.2119   $196.21   $196.20   $196.20  
  Purchase #5 $211.80   10.449%   $233.931   $233.93   $233.95   $233.90  
  Purchase #6 $86.57   10.573%   $95.723   $95.72   $95.70   $95.70  
  Purchase #7 $209.81   12.335%   $235.6901   $235.69   $235.70   $235.70  
  7 purchase totals = $1,171.92       $1,298.3655   $1,298.36   $1,298.35   $1,298.30