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 $248.63   5.726%   $262.8666   $262.87   $262.85   $262.90  
  Purchase #2 $9.59   4.325%   $10.0048   $10.00   $10.00   $10.00  
  Purchase #3 $22.77   13.689%   $25.887   $25.89   $25.90   $25.90  
  Purchase #4 $60.73   7.323%   $65.1773   $65.18   $65.20   $65.20  
  Purchase #5 $56.25   11.769%   $62.8701   $62.87   $62.85   $62.90  
  Purchase #6 $68.96   5.269%   $72.5935   $72.59   $72.60   $72.60  
  Purchase #7 $168.76   8.558%   $183.2025   $183.20   $183.20   $183.20  
  7 purchase totals = $635.69       $682.6018   $682.60   $682.60   $682.70