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 $238.58   11.509%   $266.0382   $266.04   $266.05   $266.00  
  Purchase #2 $93.33   3.792%   $96.8691   $96.87   $96.85   $96.90  
  Purchase #3 $25.57   4.629%   $26.7536   $26.75   $26.75   $26.80  
  Purchase #4 $240.93   13.401%   $273.217   $273.22   $273.20   $273.20  
  Purchase #5 $8.81   3.382%   $9.108   $9.11   $9.10   $9.10  
  Purchase #6 $229.65   9.203%   $250.7847   $250.78   $250.80   $250.80  
  Purchase #7 $26.35   4.297%   $27.4823   $27.48   $27.50   $27.50  
  7 purchase totals = $863.22       $950.2529   $950.25   $950.25   $950.30