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 $183.74   13.792%   $209.0814   $209.08   $209.10   $209.10  
  Purchase #2 $154.45   6.738%   $164.8568   $164.86   $164.85   $164.90  
  Purchase #3 $230.33   11.808%   $257.5274   $257.53   $257.55   $257.50  
  Purchase #4 $221.49   4.613%   $231.7073   $231.71   $231.70   $231.70  
  Purchase #5 $246.81   5.521%   $260.4364   $260.44   $260.45   $260.40  
  Purchase #6 $95.94   12.836%   $108.2549   $108.25   $108.25   $108.30  
  Purchase #7 $205.58   12.326%   $230.9198   $230.92   $230.90   $230.90  
  7 purchase totals = $1,338.34       $1,462.7840   $1,462.79   $1,462.80   $1,462.80