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 $203.94   11.869%   $228.1456   $228.15   $228.15   $228.10  
  Purchase #2 $48.47   8.585%   $52.6311   $52.63   $52.65   $52.60  
  Purchase #3 $21.43   5.294%   $22.5645   $22.56   $22.55   $22.60  
  Purchase #4 $206.87   9.685%   $226.9054   $226.91   $226.90   $226.90  
  Purchase #5 $68.48   11.234%   $76.173   $76.17   $76.15   $76.20  
  Purchase #6 $61.71   6.680%   $65.8322   $65.83   $65.85   $65.80  
  Purchase #7 $165.27   10.451%   $182.5424   $182.54   $182.55   $182.50  
  7 purchase totals = $776.17       $854.7942   $854.79   $854.80   $854.70