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 $61.28   9.748%   $67.2536   $67.25   $67.25   $67.30  
  Purchase #2 $222.59   11.697%   $248.6264   $248.63   $248.65   $248.60  
  Purchase #3 $51.71   11.673%   $57.7461   $57.75   $57.75   $57.70  
  Purchase #4 $171.47   13.221%   $194.14   $194.14   $194.15   $194.10  
  Purchase #5 $233.38   8.307%   $252.7669   $252.77   $252.75   $252.80  
  Purchase #6 $16.98   3.482%   $17.5712   $17.57   $17.55   $17.60  
  Purchase #7 $9.49   12.654%   $10.6909   $10.69   $10.70   $10.70  
  7 purchase totals = $766.90       $848.7951   $848.80   $848.80   $848.80