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 $225.77   11.470%   $251.6658   $251.67   $251.65   $251.70  
  Purchase #2 $68.93   4.208%   $71.8306   $71.83   $71.85   $71.80  
  Purchase #3 $115.95   6.588%   $123.5888   $123.59   $123.60   $123.60  
  Purchase #4 $33.87   4.541%   $35.408   $35.41   $35.40   $35.40  
  Purchase #5 $12.88   10.687%   $14.2565   $14.26   $14.25   $14.30  
  Purchase #6 $161.95   12.546%   $182.2682   $182.27   $182.25   $182.30  
  Purchase #7 $156.28   12.706%   $176.1369   $176.14   $176.15   $176.10  
  7 purchase totals = $775.63       $855.1548   $855.17   $855.15   $855.20