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 $183.86   13.106%   $207.9567   $207.96   $207.95   $208.00  
  Purchase #2 $77.73   6.463%   $82.7537   $82.75   $82.75   $82.80  
  Purchase #3 $20.37   5.147%   $21.4184   $21.42   $21.40   $21.40  
  Purchase #4 $197.67   9.443%   $216.336   $216.34   $216.35   $216.30  
  Purchase #5 $67.86   6.385%   $72.1929   $72.19   $72.20   $72.20  
  Purchase #6 $178.81   5.483%   $188.6142   $188.61   $188.60   $188.60  
  Purchase #7 $81.76   6.836%   $87.3491   $87.35   $87.35   $87.30  
  7 purchase totals = $808.06       $876.6210   $876.62   $876.60   $876.60