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 $198.67   4.208%   $207.03   $207.03   $207.05   $207.00  
  Purchase #2 $56.96   3.675%   $59.0533   $59.05   $59.05   $59.10  
  Purchase #3 $49.92   6.104%   $52.9671   $52.97   $52.95   $53.00  
  Purchase #4 $60.76   8.334%   $65.8237   $65.82   $65.80   $65.80  
  Purchase #5 $186.99   9.749%   $205.2197   $205.22   $205.20   $205.20  
  Purchase #6 $104.60   4.686%   $109.5016   $109.50   $109.50   $109.50  
  Purchase #7 $240.38   4.151%   $250.3582   $250.36   $250.35   $250.40  
  7 purchase totals = $898.28       $949.9536   $949.95   $949.90   $950.00