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 $97.83   3.442%   $101.1973   $101.20   $101.20   $101.20  
  Purchase #2 $15.91   4.141%   $16.5688   $16.57   $16.55   $16.60  
  Purchase #3 $217.62   3.393%   $225.0038   $225.00   $225.00   $225.00  
  Purchase #4 $182.51   10.321%   $201.3469   $201.35   $201.35   $201.30  
  Purchase #5 $195.63   13.316%   $221.6801   $221.68   $221.70   $221.70  
  Purchase #6 $145.58   6.613%   $155.2072   $155.21   $155.20   $155.20  
  Purchase #7 $69.66   4.776%   $72.987   $72.99   $73.00   $73.00  
  7 purchase totals = $924.74       $993.9911   $994.00   $994.00   $994.00