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 $216.76   11.442%   $241.5617   $241.56   $241.55   $241.60  
  Purchase #2 $148.52   6.871%   $158.7248   $158.72   $158.70   $158.70  
  Purchase #3 $30.80   10.518%   $34.0395   $34.04   $34.05   $34.00  
  Purchase #4 $54.58   10.617%   $60.3748   $60.37   $60.35   $60.40  
  Purchase #5 $117.36   6.572%   $125.0729   $125.07   $125.05   $125.10  
  Purchase #6 $250.88   5.722%   $265.2354   $265.24   $265.25   $265.20  
  Purchase #7 $34.69   8.139%   $37.5134   $37.51   $37.50   $37.50  
  7 purchase totals = $853.59       $922.5225   $922.51   $922.45   $922.50