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 $211.61   7.227%   $226.9031   $226.90   $226.90   $226.90  
  Purchase #2 $127.41   13.379%   $144.4562   $144.46   $144.45   $144.50  
  Purchase #3 $241.34   11.350%   $268.7321   $268.73   $268.75   $268.70  
  Purchase #4 $177.86   10.116%   $195.8523   $195.85   $195.85   $195.90  
  Purchase #5 $12.34   6.481%   $13.1398   $13.14   $13.15   $13.10  
  Purchase #6 $46.31   8.702%   $50.3399   $50.34   $50.35   $50.30  
  Purchase #7 $178.63   12.675%   $201.2714   $201.27   $201.25   $201.30  
  7 purchase totals = $995.50       $1,100.6948   $1,100.69   $1,100.70   $1,100.70