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 $60.41   6.126%   $64.1107   $64.11   $64.10   $64.10  
  Purchase #2 $196.41   5.597%   $207.4031   $207.40   $207.40   $207.40  
  Purchase #3 $51.88   4.617%   $54.2753   $54.28   $54.30   $54.30  
  Purchase #4 $131.52   3.841%   $136.5717   $136.57   $136.55   $136.60  
  Purchase #5 $26.25   6.489%   $27.9534   $27.95   $27.95   $28.00  
  Purchase #6 $109.80   4.176%   $114.3852   $114.39   $114.40   $114.40  
  Purchase #7 $155.78   6.838%   $166.4322   $166.43   $166.45   $166.40  
  7 purchase totals = $732.05       $771.1316   $771.13   $771.15   $771.20