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 $24.90   5.118%   $26.1744   $26.17   $26.15   $26.20  
  Purchase #2 $213.42   9.534%   $233.7675   $233.77   $233.75   $233.80  
  Purchase #3 $112.64   13.309%   $127.6313   $127.63   $127.65   $127.60  
  Purchase #4 $116.50   8.142%   $125.9854   $125.99   $126.00   $126.00  
  Purchase #5 $57.39   13.338%   $65.0447   $65.04   $65.05   $65.00  
  Purchase #6 $190.25   10.209%   $209.6726   $209.67   $209.65   $209.70  
  Purchase #7 $65.94   10.364%   $72.774   $72.77   $72.75   $72.80  
  7 purchase totals = $781.04       $861.0499   $861.04   $861.00   $861.10