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 $208.45   8.488%   $226.1432   $226.14   $226.15   $226.10  
  Purchase #2 $44.81   12.368%   $50.3521   $50.35   $50.35   $50.40  
  Purchase #3 $171.42   10.731%   $189.8151   $189.82   $189.80   $189.80  
  Purchase #4 $79.75   3.407%   $82.4671   $82.47   $82.45   $82.50  
  Purchase #5 $163.64   12.271%   $183.7203   $183.72   $183.70   $183.70  
  Purchase #6 $26.45   6.155%   $28.078   $28.08   $28.10   $28.10  
  Purchase #7 $119.70   3.614%   $124.026   $124.03   $124.05   $124.00  
  7 purchase totals = $814.22       $884.6018   $884.61   $884.60   $884.60