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 $214.67   9.635%   $235.3535   $235.35   $235.35   $235.40  
  Purchase #2 $26.37   8.307%   $28.5606   $28.56   $28.55   $28.60  
  Purchase #3 $95.29   8.244%   $103.1457   $103.15   $103.15   $103.10  
  Purchase #4 $242.51   8.530%   $263.1961   $263.20   $263.20   $263.20  
  Purchase #5 $68.45   12.595%   $77.0713   $77.07   $77.05   $77.10  
  Purchase #6 $121.25   11.571%   $135.2798   $135.28   $135.30   $135.30  
  Purchase #7 $116.39   8.790%   $126.6207   $126.62   $126.60   $126.60  
  7 purchase totals = $884.93       $969.2277   $969.23   $969.20   $969.30