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 $82.55   11.869%   $92.3479   $92.35   $92.35   $92.30  
  Purchase #2 $152.86   5.626%   $161.4599   $161.46   $161.45   $161.50  
  Purchase #3 $213.26   13.476%   $241.9989   $242.00   $242.00   $242.00  
  Purchase #4 $29.99   7.177%   $32.1424   $32.14   $32.15   $32.10  
  Purchase #5 $65.36   11.198%   $72.679   $72.68   $72.70   $72.70  
  Purchase #6 $248.59   6.131%   $263.8311   $263.83   $263.85   $263.80  
  Purchase #7 $208.40   10.493%   $230.2674   $230.27   $230.25   $230.30  
  7 purchase totals = $1,001.01       $1,094.7266   $1,094.73   $1,094.75   $1,094.70