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 $224.27   11.696%   $250.5006   $250.50   $250.50   $250.50  
  Purchase #2 $122.82   3.774%   $127.4552   $127.46   $127.45   $127.50  
  Purchase #3 $141.94   5.724%   $150.0646   $150.06   $150.05   $150.10  
  Purchase #4 $187.41   5.224%   $197.2003   $197.20   $197.20   $197.20  
  Purchase #5 $67.86   11.598%   $75.7304   $75.73   $75.75   $75.70  
  Purchase #6 $120.97   11.612%   $135.017   $135.02   $135.00   $135.00  
  Purchase #7 $237.91   8.457%   $258.03   $258.03   $258.05   $258.00  
  7 purchase totals = $1,103.18       $1,193.9981   $1,194.00   $1,194.00   $1,194.00