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 $71.31   4.109%   $74.2401   $74.24   $74.25   $74.20  
  Purchase #2 $206.37   5.661%   $218.0526   $218.05   $218.05   $218.10  
  Purchase #3 $180.28   11.357%   $200.7544   $200.75   $200.75   $200.80  
  Purchase #4 $195.68   6.675%   $208.7416   $208.74   $208.75   $208.70  
  Purchase #5 $8.75   7.416%   $9.3989   $9.40   $9.40   $9.40  
  Purchase #6 $243.67   10.330%   $268.8411   $268.84   $268.85   $268.80  
  Purchase #7 $87.63   8.423%   $95.0111   $95.01   $95.00   $95.00  
  7 purchase totals = $993.69       $1,075.0398   $1,075.03   $1,075.05   $1,075.00