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 $61.39   5.398%   $64.7038   $64.70   $64.70   $64.70  
  Purchase #2 $97.75   3.168%   $100.8467   $100.85   $100.85   $100.80  
  Purchase #3 $108.46   5.196%   $114.0956   $114.10   $114.10   $114.10  
  Purchase #4 $35.37   4.354%   $36.91   $36.91   $36.90   $36.90  
  Purchase #5 $58.64   4.856%   $61.4876   $61.49   $61.50   $61.50  
  Purchase #6 $39.67   3.226%   $40.9498   $40.95   $40.95   $40.90  
  Purchase #7 $198.39   7.107%   $212.4896   $212.49   $212.50   $212.50  
  7 purchase totals = $599.67       $631.4831   $631.49   $631.50   $631.40