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 $248.31   11.393%   $276.6   $276.60   $276.60   $276.60  
  Purchase #2 $30.44   11.473%   $33.9324   $33.93   $33.95   $33.90  
  Purchase #3 $146.90   3.502%   $152.0444   $152.04   $152.05   $152.00  
  Purchase #4 $13.63   13.222%   $15.4322   $15.43   $15.45   $15.40  
  Purchase #5 $111.69   3.711%   $115.8348   $115.83   $115.85   $115.80  
  Purchase #6 $179.74   12.138%   $201.5568   $201.56   $201.55   $201.60  
  Purchase #7 $244.40   6.675%   $260.7137   $260.71   $260.70   $260.70  
  7 purchase totals = $975.11       $1,056.1143   $1,056.10   $1,056.15   $1,056.00