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 $248.68   11.772%   $277.9546   $277.95   $277.95   $278.00  
  Purchase #2 $42.43   13.139%   $48.0049   $48.00   $48.00   $48.00  
  Purchase #3 $146.79   8.238%   $158.8826   $158.88   $158.90   $158.90  
  Purchase #4 $250.78   11.126%   $278.6818   $278.68   $278.70   $278.70  
  Purchase #5 $53.74   11.347%   $59.8379   $59.84   $59.85   $59.80  
  Purchase #6 $199.63   12.364%   $224.3123   $224.31   $224.30   $224.30  
  Purchase #7 $72.60   4.118%   $75.5897   $75.59   $75.60   $75.60  
  7 purchase totals = $1,014.65       $1,123.2638   $1,123.25   $1,123.30   $1,123.30