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 $60.52   3.633%   $62.7187   $62.72   $62.70   $62.70  
  Purchase #2 $146.47   5.415%   $154.4014   $154.40   $154.40   $154.40  
  Purchase #3 $122.80   9.385%   $134.3248   $134.32   $134.30   $134.30  
  Purchase #4 $201.27   12.696%   $226.8232   $226.82   $226.80   $226.80  
  Purchase #5 $53.61   12.590%   $60.3595   $60.36   $60.35   $60.40  
  Purchase #6 $24.64   6.531%   $26.2492   $26.25   $26.25   $26.20  
  Purchase #7 $105.50   8.422%   $114.3852   $114.39   $114.40   $114.40  
  7 purchase totals = $714.81       $779.2620   $779.26   $779.20   $779.20