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 $24.89   6.866%   $26.5989   $26.60   $26.60   $26.60  
  Purchase #2 $106.92   4.451%   $111.679   $111.68   $111.70   $111.70  
  Purchase #3 $234.29   9.370%   $256.243   $256.24   $256.25   $256.20  
  Purchase #4 $185.98   9.643%   $203.9141   $203.91   $203.90   $203.90  
  Purchase #5 $176.65   11.289%   $196.592   $196.59   $196.60   $196.60  
  Purchase #6 $170.63   10.805%   $189.0666   $189.07   $189.05   $189.10  
  Purchase #7 $239.26   12.140%   $268.3062   $268.31   $268.30   $268.30  
  7 purchase totals = $1,138.62       $1,252.3998   $1,252.40   $1,252.40   $1,252.40