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 $93.58   5.423%   $98.6548   $98.65   $98.65   $98.70  
  Purchase #2 $40.90   3.546%   $42.3503   $42.35   $42.35   $42.40  
  Purchase #3 $247.62   12.166%   $277.7454   $277.75   $277.75   $277.70  
  Purchase #4 $177.99   8.253%   $192.6795   $192.68   $192.70   $192.70  
  Purchase #5 $153.58   11.373%   $171.0467   $171.05   $171.05   $171.00  
  Purchase #6 $34.84   3.755%   $36.1482   $36.15   $36.15   $36.10  
  Purchase #7 $26.47   5.517%   $27.9303   $27.93   $27.95   $27.90  
  7 purchase totals = $774.98       $846.5552   $846.56   $846.60   $846.50