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 $221.99   5.853%   $234.9831   $234.98   $235.00   $235.00  
  Purchase #2 $104.82   12.444%   $117.8638   $117.86   $117.85   $117.90  
  Purchase #3 $121.61   13.572%   $138.1149   $138.11   $138.10   $138.10  
  Purchase #4 $161.61   8.248%   $174.9396   $174.94   $174.95   $174.90  
  Purchase #5 $82.60   3.795%   $85.7347   $85.73   $85.75   $85.70  
  Purchase #6 $230.63   12.147%   $258.6446   $258.64   $258.65   $258.60  
  Purchase #7 $219.69   13.860%   $250.139   $250.14   $250.15   $250.10  
  7 purchase totals = $1,142.95       $1,260.4197   $1,260.40   $1,260.45   $1,260.30