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 $56.61   8.824%   $61.6053   $61.61   $61.60   $61.60  
  Purchase #2 $216.38   12.410%   $243.2328   $243.23   $243.25   $243.20  
  Purchase #3 $27.41   5.347%   $28.8756   $28.88   $28.90   $28.90  
  Purchase #4 $65.65   9.308%   $71.7607   $71.76   $71.75   $71.80  
  Purchase #5 $200.38   3.279%   $206.9505   $206.95   $206.95   $207.00  
  Purchase #6 $173.92   7.155%   $186.364   $186.36   $186.35   $186.40  
  Purchase #7 $232.59   11.531%   $259.41   $259.41   $259.40   $259.40  
  7 purchase totals = $972.94       $1,058.1989   $1,058.20   $1,058.20   $1,058.30