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 $200.44   11.583%   $223.657   $223.66   $223.65   $223.70  
  Purchase #2 $80.27   10.477%   $88.6799   $88.68   $88.70   $88.70  
  Purchase #3 $60.68   12.627%   $68.3421   $68.34   $68.35   $68.30  
  Purchase #4 $51.99   11.595%   $58.0182   $58.02   $58.00   $58.00  
  Purchase #5 $183.53   12.169%   $205.8638   $205.86   $205.85   $205.90  
  Purchase #6 $62.27   12.335%   $69.951   $69.95   $69.95   $70.00  
  Purchase #7 $75.90   8.668%   $82.479   $82.48   $82.50   $82.50  
  7 purchase totals = $715.08       $796.9910   $796.99   $797.00   $797.10