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 $226.74   5.419%   $239.027   $239.03   $239.05   $239.00  
  Purchase #2 $15.28   13.816%   $17.3911   $17.39   $17.40   $17.40  
  Purchase #3 $224.32   3.332%   $231.7943   $231.79   $231.80   $231.80  
  Purchase #4 $156.92   5.244%   $165.1489   $165.15   $165.15   $165.10  
  Purchase #5 $64.68   5.815%   $68.4411   $68.44   $68.45   $68.40  
  Purchase #6 $194.72   3.622%   $201.7728   $201.77   $201.75   $201.80  
  Purchase #7 $242.44   8.349%   $262.6813   $262.68   $262.70   $262.70  
  7 purchase totals = $1,125.10       $1,186.2565   $1,186.25   $1,186.30   $1,186.20