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 $241.48   10.496%   $266.8257   $266.83   $266.85   $266.80  
  Purchase #2 $86.70   11.435%   $96.6141   $96.61   $96.60   $96.60  
  Purchase #3 $67.67   4.437%   $70.6725   $70.67   $70.65   $70.70  
  Purchase #4 $48.88   10.795%   $54.1566   $54.16   $54.15   $54.20  
  Purchase #5 $177.35   9.277%   $193.8028   $193.80   $193.80   $193.80  
  Purchase #6 $56.58   3.659%   $58.6503   $58.65   $58.65   $58.70  
  Purchase #7 $242.37   4.319%   $252.838   $252.84   $252.85   $252.80  
  7 purchase totals = $921.03       $993.5600   $993.56   $993.55   $993.60