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 $208.76   9.697%   $229.0035   $229.00   $229.00   $229.00  
  Purchase #2 $213.57   5.307%   $224.9042   $224.90   $224.90   $224.90  
  Purchase #3 $68.77   11.747%   $76.8484   $76.85   $76.85   $76.80  
  Purchase #4 $202.63   4.326%   $211.3958   $211.40   $211.40   $211.40  
  Purchase #5 $118.27   3.201%   $122.0558   $122.06   $122.05   $122.10  
  Purchase #6 $193.83   10.521%   $214.2229   $214.22   $214.20   $214.20  
  Purchase #7 $111.81   11.372%   $124.525   $124.53   $124.55   $124.50  
  7 purchase totals = $1,117.64       $1,202.9556   $1,202.96   $1,202.95   $1,202.90