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 $61.35   12.576%   $69.0654   $69.07   $69.05   $69.10  
  Purchase #2 $60.66   4.581%   $63.4388   $63.44   $63.45   $63.40  
  Purchase #3 $204.58   3.509%   $211.7587   $211.76   $211.75   $211.80  
  Purchase #4 $97.83   12.107%   $109.6743   $109.67   $109.65   $109.70  
  Purchase #5 $221.32   8.364%   $239.8312   $239.83   $239.85   $239.80  
  Purchase #6 $13.83   13.830%   $15.7427   $15.74   $15.75   $15.70  
  Purchase #7 $221.33   5.804%   $234.176   $234.18   $234.20   $234.20  
  7 purchase totals = $880.90       $943.6871   $943.69   $943.70   $943.70