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 $81.88   11.316%   $91.1455   $91.15   $91.15   $91.10  
  Purchase #2 $180.86   8.452%   $196.1463   $196.15   $196.15   $196.10  
  Purchase #3 $155.34   5.563%   $163.9816   $163.98   $164.00   $164.00  
  Purchase #4 $220.33   7.106%   $235.9866   $235.99   $236.00   $236.00  
  Purchase #5 $33.37   9.120%   $36.4133   $36.41   $36.40   $36.40  
  Purchase #6 $215.62   6.795%   $230.2714   $230.27   $230.25   $230.30  
  Purchase #7 $62.93   11.575%   $70.2141   $70.21   $70.20   $70.20  
  7 purchase totals = $950.33       $1,024.1588   $1,024.16   $1,024.15   $1,024.10