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 $61.57   10.707%   $68.1623   $68.16   $68.15   $68.20  
  Purchase #2 $46.96   11.674%   $52.4421   $52.44   $52.45   $52.40  
  Purchase #3 $78.90   9.195%   $86.1549   $86.15   $86.15   $86.20  
  Purchase #4 $104.40   4.409%   $109.003   $109.00   $109.00   $109.00  
  Purchase #5 $108.45   13.176%   $122.7394   $122.74   $122.75   $122.70  
  Purchase #6 $201.79   5.621%   $213.1326   $213.13   $213.15   $213.10  
  Purchase #7 $236.97   12.483%   $266.551   $266.55   $266.55   $266.60  
  7 purchase totals = $839.04       $918.1853   $918.17   $918.20   $918.20