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 $66.88   6.177%   $71.0112   $71.01   $71.00   $71.00  
  Purchase #2 $166.76   10.702%   $184.6067   $184.61   $184.60   $184.60  
  Purchase #3 $86.60   13.351%   $98.162   $98.16   $98.15   $98.20  
  Purchase #4 $169.96   13.797%   $193.4094   $193.41   $193.40   $193.40  
  Purchase #5 $208.68   5.753%   $220.6854   $220.69   $220.70   $220.70  
  Purchase #6 $172.68   5.731%   $182.5763   $182.58   $182.60   $182.60  
  Purchase #7 $13.53   3.738%   $14.0358   $14.04   $14.05   $14.00  
  7 purchase totals = $885.09       $964.4868   $964.50   $964.50   $964.50