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 $87.90   11.720%   $98.2019   $98.20   $98.20   $98.20  
  Purchase #2 $115.53   3.764%   $119.8785   $119.88   $119.90   $119.90  
  Purchase #3 $131.48   6.690%   $140.276   $140.28   $140.30   $140.30  
  Purchase #4 $218.69   11.107%   $242.9799   $242.98   $243.00   $243.00  
  Purchase #5 $174.76   4.711%   $182.9929   $182.99   $183.00   $183.00  
  Purchase #6 $208.43   9.821%   $228.8999   $228.90   $228.90   $228.90  
  Purchase #7 $84.35   10.527%   $93.2295   $93.23   $93.25   $93.20  
  7 purchase totals = $1,021.14       $1,106.4586   $1,106.46   $1,106.55   $1,106.50