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 $206.61   3.607%   $214.0624   $214.06   $214.05   $214.10  
  Purchase #2 $104.57   11.431%   $116.5234   $116.52   $116.50   $116.50  
  Purchase #3 $47.61   9.635%   $52.1972   $52.20   $52.20   $52.20  
  Purchase #4 $202.39   6.358%   $215.258   $215.26   $215.25   $215.30  
  Purchase #5 $25.63   6.129%   $27.2009   $27.20   $27.20   $27.20  
  Purchase #6 $235.59   11.575%   $262.8595   $262.86   $262.85   $262.90  
  Purchase #7 $61.25   9.579%   $67.1171   $67.12   $67.10   $67.10  
  7 purchase totals = $883.65       $955.2185   $955.22   $955.15   $955.30