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 $224.78   13.291%   $254.6555   $254.66   $254.65   $254.70  
  Purchase #2 $158.56   11.267%   $176.425   $176.43   $176.45   $176.40  
  Purchase #3 $55.96   13.419%   $63.4693   $63.47   $63.45   $63.50  
  Purchase #4 $129.67   4.575%   $135.6024   $135.60   $135.60   $135.60  
  Purchase #5 $241.87   5.192%   $254.4279   $254.43   $254.45   $254.40  
  Purchase #6 $225.48   12.828%   $254.4046   $254.40   $254.40   $254.40  
  Purchase #7 $246.99   10.494%   $272.9091   $272.91   $272.90   $272.90  
  7 purchase totals = $1,283.31       $1,411.8938   $1,411.90   $1,411.90   $1,411.90