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 $163.48   12.763%   $184.345   $184.35   $184.35   $184.30  
  Purchase #2 $207.65   10.713%   $229.8955   $229.90   $229.90   $229.90  
  Purchase #3 $62.98   12.325%   $70.7423   $70.74   $70.75   $70.70  
  Purchase #4 $10.70   8.299%   $11.588   $11.59   $11.60   $11.60  
  Purchase #5 $24.56   11.557%   $27.3984   $27.40   $27.40   $27.40  
  Purchase #6 $107.25   7.733%   $115.5436   $115.54   $115.55   $115.50  
  Purchase #7 $144.78   7.857%   $156.1554   $156.16   $156.15   $156.20  
  7 purchase totals = $721.40       $795.6682   $795.68   $795.70   $795.60