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 $208.57   7.452%   $224.1126   $224.11   $224.10   $224.10  
  Purchase #2 $187.81   4.467%   $196.1995   $196.20   $196.20   $196.20  
  Purchase #3 $83.59   12.722%   $94.2243   $94.22   $94.20   $94.20  
  Purchase #4 $90.79   3.192%   $93.688   $93.69   $93.70   $93.70  
  Purchase #5 $10.35   8.853%   $11.2663   $11.27   $11.25   $11.30  
  Purchase #6 $95.72   9.253%   $104.577   $104.58   $104.60   $104.60  
  Purchase #7 $122.44   8.802%   $133.2172   $133.22   $133.20   $133.20  
  7 purchase totals = $799.27       $857.2849   $857.29   $857.25   $857.30