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 $90.95   12.128%   $101.9804   $101.98   $102.00   $102.00  
  Purchase #2 $60.59   3.232%   $62.5483   $62.55   $62.55   $62.50  
  Purchase #3 $115.36   3.861%   $119.814   $119.81   $119.80   $119.80  
  Purchase #4 $56.35   12.439%   $63.3594   $63.36   $63.35   $63.40  
  Purchase #5 $154.81   13.386%   $175.5329   $175.53   $175.55   $175.50  
  Purchase #6 $168.97   5.677%   $178.5624   $178.56   $178.55   $178.60  
  Purchase #7 $236.39   13.476%   $268.2459   $268.25   $268.25   $268.20  
  7 purchase totals = $883.42       $970.0433   $970.04   $970.05   $970.00