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 $182.84   13.600%   $207.7062   $207.71   $207.70   $207.70  
  Purchase #2 $168.36   4.733%   $176.3285   $176.33   $176.35   $176.30  
  Purchase #3 $154.97   11.715%   $173.1247   $173.12   $173.10   $173.10  
  Purchase #4 $121.42   10.830%   $134.5698   $134.57   $134.55   $134.60  
  Purchase #5 $22.69   11.169%   $25.2242   $25.22   $25.20   $25.20  
  Purchase #6 $103.90   5.293%   $109.3994   $109.40   $109.40   $109.40  
  Purchase #7 $154.45   10.241%   $170.2672   $170.27   $170.25   $170.30  
  7 purchase totals = $908.63       $996.6200   $996.62   $996.55   $996.60