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 $86.67   9.722%   $95.0961   $95.10   $95.10   $95.10  
  Purchase #2 $126.91   10.650%   $140.4259   $140.43   $140.45   $140.40  
  Purchase #3 $11.78   4.358%   $12.2934   $12.29   $12.30   $12.30  
  Purchase #4 $206.88   13.427%   $234.6578   $234.66   $234.65   $234.70  
  Purchase #5 $125.48   7.845%   $135.3239   $135.32   $135.30   $135.30  
  Purchase #6 $248.44   3.595%   $257.3714   $257.37   $257.35   $257.40  
  Purchase #7 $21.69   3.792%   $22.5125   $22.51   $22.50   $22.50  
  7 purchase totals = $827.85       $897.6810   $897.68   $897.65   $897.70