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 $73.76   6.591%   $78.6215   $78.62   $78.60   $78.60  
  Purchase #2 $194.40   8.581%   $211.0815   $211.08   $211.10   $211.10  
  Purchase #3 $120.43   13.126%   $136.2376   $136.24   $136.25   $136.20  
  Purchase #4 $96.26   10.795%   $106.6513   $106.65   $106.65   $106.70  
  Purchase #5 $13.42   4.830%   $14.0682   $14.07   $14.05   $14.10  
  Purchase #6 $208.84   8.671%   $226.9485   $226.95   $226.95   $226.90  
  Purchase #7 $105.88   7.143%   $113.443   $113.44   $113.45   $113.40  
  7 purchase totals = $812.99       $887.0516   $887.05   $887.05   $887.00