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 $248.60   5.626%   $262.5862   $262.59   $262.60   $262.60  
  Purchase #2 $177.51   13.241%   $201.0141   $201.01   $201.00   $201.00  
  Purchase #3 $101.54   4.793%   $106.4068   $106.41   $106.40   $106.40  
  Purchase #4 $72.82   11.197%   $80.9737   $80.97   $80.95   $81.00  
  Purchase #5 $63.32   3.371%   $65.4545   $65.45   $65.45   $65.50  
  Purchase #6 $206.61   9.295%   $225.8144   $225.81   $225.80   $225.80  
  Purchase #7 $83.96   4.477%   $87.7189   $87.72   $87.70   $87.70  
  7 purchase totals = $954.36       $1,029.9686   $1,029.96   $1,029.90   $1,030.00