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 $201.56   11.201%   $224.1367   $224.14   $224.15   $224.10  
  Purchase #2 $7.98   7.630%   $8.5889   $8.59   $8.60   $8.60  
  Purchase #3 $206.57   6.769%   $220.5527   $220.55   $220.55   $220.60  
  Purchase #4 $233.77   8.617%   $253.914   $253.91   $253.90   $253.90  
  Purchase #5 $53.35   8.698%   $57.9904   $57.99   $58.00   $58.00  
  Purchase #6 $114.66   3.611%   $118.8004   $118.80   $118.80   $118.80  
  Purchase #7 $87.58   11.166%   $97.3592   $97.36   $97.35   $97.40  
  7 purchase totals = $905.47       $981.3423   $981.34   $981.35   $981.40