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 $30.52   13.567%   $34.6606   $34.66   $34.65   $34.70  
  Purchase #2 $104.65   12.341%   $117.5649   $117.56   $117.55   $117.60  
  Purchase #3 $115.83   9.103%   $126.374   $126.37   $126.35   $126.40  
  Purchase #4 $168.29   9.523%   $184.3163   $184.32   $184.30   $184.30  
  Purchase #5 $43.35   6.624%   $46.2215   $46.22   $46.20   $46.20  
  Purchase #6 $65.60   13.430%   $74.4101   $74.41   $74.40   $74.40  
  Purchase #7 $123.57   8.137%   $133.6249   $133.62   $133.60   $133.60  
  7 purchase totals = $651.81       $717.1723   $717.16   $717.05   $717.20