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 $61.30   13.606%   $69.6405   $69.64   $69.65   $69.60  
  Purchase #2 $105.39   10.860%   $116.8354   $116.84   $116.85   $116.80  
  Purchase #3 $114.69   9.161%   $125.1968   $125.20   $125.20   $125.20  
  Purchase #4 $176.51   12.770%   $199.0503   $199.05   $199.05   $199.10  
  Purchase #5 $65.90   7.202%   $70.6461   $70.65   $70.65   $70.60  
  Purchase #6 $142.33   5.654%   $150.3773   $150.38   $150.40   $150.40  
  Purchase #7 $97.66   7.483%   $104.9679   $104.97   $104.95   $105.00  
  7 purchase totals = $763.78       $836.7143   $836.73   $836.75   $836.70