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 $103.74   10.111%   $114.2292   $114.23   $114.25   $114.20  
  Purchase #2 $185.54   12.434%   $208.61   $208.61   $208.60   $208.60  
  Purchase #3 $23.55   13.461%   $26.7201   $26.72   $26.70   $26.70  
  Purchase #4 $133.93   7.220%   $143.5997   $143.60   $143.60   $143.60  
  Purchase #5 $180.73   7.593%   $194.4528   $194.45   $194.45   $194.50  
  Purchase #6 $134.96   13.639%   $153.3672   $153.37   $153.35   $153.40  
  Purchase #7 $61.52   3.818%   $63.8688   $63.87   $63.85   $63.90  
  7 purchase totals = $823.97       $904.8478   $904.85   $904.80   $904.90