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 $188.59   9.663%   $206.8135   $206.81   $206.80   $206.80  
  Purchase #2 $176.43   12.157%   $197.8786   $197.88   $197.90   $197.90  
  Purchase #3 $97.70   12.661%   $110.0698   $110.07   $110.05   $110.10  
  Purchase #4 $241.99   3.419%   $250.2636   $250.26   $250.25   $250.30  
  Purchase #5 $44.49   11.649%   $49.6726   $49.67   $49.65   $49.70  
  Purchase #6 $82.64   4.316%   $86.2067   $86.21   $86.20   $86.20  
  Purchase #7 $98.58   13.490%   $111.8784   $111.88   $111.90   $111.90  
  7 purchase totals = $930.42       $1,012.7832   $1,012.78   $1,012.75   $1,012.90