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 $183.41   10.118%   $201.9674   $201.97   $201.95   $202.00  
  Purchase #2 $20.91   8.256%   $22.6363   $22.64   $22.65   $22.60  
  Purchase #3 $144.49   9.706%   $158.5142   $158.51   $158.50   $158.50  
  Purchase #4 $148.78   5.542%   $157.0254   $157.03   $157.05   $157.00  
  Purchase #5 $6.69   6.188%   $7.104   $7.10   $7.10   $7.10  
  Purchase #6 $184.61   3.340%   $190.776   $190.78   $190.80   $190.80  
  Purchase #7 $184.82   7.329%   $198.3655   $198.37   $198.35   $198.40  
  7 purchase totals = $873.71       $936.3888   $936.40   $936.40   $936.40