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 $61.45   7.331%   $65.9549   $65.95   $65.95   $66.00  
  Purchase #2 $37.78   10.242%   $41.6494   $41.65   $41.65   $41.60  
  Purchase #3 $156.43   13.775%   $177.9782   $177.98   $178.00   $178.00  
  Purchase #4 $26.34   3.124%   $27.1629   $27.16   $27.15   $27.20  
  Purchase #5 $98.89   5.309%   $104.1401   $104.14   $104.15   $104.10  
  Purchase #6 $187.67   11.547%   $209.3403   $209.34   $209.35   $209.30  
  Purchase #7 $241.86   8.835%   $263.2283   $263.23   $263.25   $263.20  
  7 purchase totals = $810.42       $889.4541   $889.45   $889.50   $889.40