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 $62.72   8.433%   $68.0092   $68.01   $68.00   $68.00  
  Purchase #2 $151.57   6.322%   $161.1523   $161.15   $161.15   $161.20  
  Purchase #3 $218.59   4.419%   $228.2495   $228.25   $228.25   $228.20  
  Purchase #4 $123.30   13.733%   $140.2328   $140.23   $140.25   $140.20  
  Purchase #5 $52.55   10.641%   $58.1418   $58.14   $58.15   $58.10  
  Purchase #6 $98.79   3.646%   $102.3919   $102.39   $102.40   $102.40  
  Purchase #7 $60.96   4.493%   $63.6989   $63.70   $63.70   $63.70  
  7 purchase totals = $768.48       $821.8764   $821.87   $821.90   $821.80