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 $109.27   13.293%   $123.7953   $123.80   $123.80   $123.80  
  Purchase #2 $230.57   3.158%   $237.8514   $237.85   $237.85   $237.90  
  Purchase #3 $245.82   12.567%   $276.7122   $276.71   $276.70   $276.70  
  Purchase #4 $93.53   4.602%   $97.8343   $97.83   $97.85   $97.80  
  Purchase #5 $200.74   13.709%   $228.2594   $228.26   $228.25   $228.30  
  Purchase #6 $239.37   5.438%   $252.3869   $252.39   $252.40   $252.40  
  Purchase #7 $39.47   10.800%   $43.7328   $43.73   $43.75   $43.70  
  7 purchase totals = $1,158.77       $1,260.5723   $1,260.57   $1,260.60   $1,260.60