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 $56.94   9.187%   $62.1711   $62.17   $62.15   $62.20  
  Purchase #2 $144.98   6.202%   $153.9717   $153.97   $153.95   $154.00  
  Purchase #3 $8.52   8.663%   $9.2581   $9.26   $9.25   $9.30  
  Purchase #4 $157.33   9.206%   $171.8138   $171.81   $171.80   $171.80  
  Purchase #5 $220.92   9.516%   $241.9427   $241.94   $241.95   $241.90  
  Purchase #6 $85.44   12.325%   $95.9705   $95.97   $95.95   $96.00  
  Purchase #7 $208.68   3.848%   $216.71   $216.71   $216.70   $216.70  
  7 purchase totals = $882.81       $951.8379   $951.83   $951.75   $951.90