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 $218.81   8.145%   $236.6321   $236.63   $236.65   $236.60  
  Purchase #2 $51.79   7.664%   $55.7592   $55.76   $55.75   $55.80  
  Purchase #3 $110.73   12.256%   $124.3011   $124.30   $124.30   $124.30  
  Purchase #4 $200.62   13.548%   $227.8   $227.80   $227.80   $227.80  
  Purchase #5 $247.71   7.805%   $267.0438   $267.04   $267.05   $267.00  
  Purchase #6 $43.91   12.560%   $49.4251   $49.43   $49.45   $49.40  
  Purchase #7 $138.49   13.705%   $157.4701   $157.47   $157.45   $157.50  
  7 purchase totals = $1,012.06       $1,118.4314   $1,118.43   $1,118.45   $1,118.40