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 $61.86   6.308%   $65.7621   $65.76   $65.75   $65.80  
  Purchase #2 $148.35   9.271%   $162.1035   $162.10   $162.10   $162.10  
  Purchase #3 $79.25   3.689%   $82.1735   $82.17   $82.15   $82.20  
  Purchase #4 $50.72   12.267%   $56.9418   $56.94   $56.95   $56.90  
  Purchase #5 $187.57   12.798%   $211.5752   $211.58   $211.60   $211.60  
  Purchase #6 $126.93   5.245%   $133.5875   $133.59   $133.60   $133.60  
  Purchase #7 $188.27   10.179%   $207.434   $207.43   $207.45   $207.40  
  7 purchase totals = $842.95       $919.5776   $919.57   $919.60   $919.60