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 $211.72   11.756%   $236.6098   $236.61   $236.60   $236.60  
  Purchase #2 $80.91   6.479%   $86.1522   $86.15   $86.15   $86.20  
  Purchase #3 $233.39   4.311%   $243.4514   $243.45   $243.45   $243.50  
  Purchase #4 $226.28   4.584%   $236.6527   $236.65   $236.65   $236.70  
  Purchase #5 $209.69   11.702%   $234.2279   $234.23   $234.25   $234.20  
  Purchase #6 $97.42   8.583%   $105.7816   $105.78   $105.80   $105.80  
  Purchase #7 $250.87   13.431%   $284.5643   $284.56   $284.55   $284.60  
  7 purchase totals = $1,310.28       $1,427.4399   $1,427.43   $1,427.45   $1,427.60