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 $235.41   5.767%   $248.9861   $248.99   $249.00   $249.00  
  Purchase #2 $119.46   4.418%   $124.7377   $124.74   $124.75   $124.70  
  Purchase #3 $238.26   7.366%   $255.8102   $255.81   $255.80   $255.80  
  Purchase #4 $62.89   9.230%   $68.6947   $68.69   $68.70   $68.70  
  Purchase #5 $248.27   8.834%   $270.2022   $270.20   $270.20   $270.20  
  Purchase #6 $169.48   11.394%   $188.7906   $188.79   $188.80   $188.80  
  Purchase #7 $192.75   4.216%   $200.8763   $200.88   $200.90   $200.90  
  7 purchase totals = $1,266.52       $1,358.0978   $1,358.10   $1,358.15   $1,358.10