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 $248.54   5.534%   $262.2942   $262.29   $262.30   $262.30  
  Purchase #2 $224.61   3.829%   $233.2103   $233.21   $233.20   $233.20  
  Purchase #3 $207.78   13.392%   $235.6059   $235.61   $235.60   $235.60  
  Purchase #4 $23.71   9.369%   $25.9314   $25.93   $25.95   $25.90  
  Purchase #5 $38.34   6.351%   $40.775   $40.78   $40.80   $40.80  
  Purchase #6 $98.45   6.437%   $104.7872   $104.79   $104.80   $104.80  
  Purchase #7 $129.81   5.209%   $136.5718   $136.57   $136.55   $136.60  
  7 purchase totals = $971.24       $1,039.1758   $1,039.18   $1,039.20   $1,039.20