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   11.403%   $277.037   $277.04   $277.05   $277.00  
  Purchase #2 $34.57   12.822%   $39.0026   $39.00   $39.00   $39.00  
  Purchase #3 $164.44   12.162%   $184.4392   $184.44   $184.45   $184.40  
  Purchase #4 $250.44   5.450%   $264.089   $264.09   $264.10   $264.10  
  Purchase #5 $90.60   3.342%   $93.6279   $93.63   $93.65   $93.60  
  Purchase #6 $169.87   5.537%   $179.2757   $179.28   $179.30   $179.30  
  Purchase #7 $53.92   10.391%   $59.5228   $59.52   $59.50   $59.50  
  7 purchase totals = $1,012.52       $1,096.9942   $1,097.00   $1,097.05   $1,096.90