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 $108.82   10.208%   $119.9283   $119.93   $119.95   $119.90  
  Purchase #2 $127.27   12.259%   $142.872   $142.87   $142.85   $142.90  
  Purchase #3 $201.84   7.541%   $217.0608   $217.06   $217.05   $217.10  
  Purchase #4 $16.28   4.761%   $17.0551   $17.06   $17.05   $17.10  
  Purchase #5 $89.95   9.298%   $98.3136   $98.31   $98.30   $98.30  
  Purchase #6 $115.74   5.609%   $122.2319   $122.23   $122.25   $122.20  
  Purchase #7 $104.54   11.296%   $116.3488   $116.35   $116.35   $116.30  
  7 purchase totals = $764.44       $833.8105   $833.81   $833.80   $833.80