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 $23.32   11.449%   $25.9899   $25.99   $26.00   $26.00  
  Purchase #2 $97.61   9.104%   $106.4964   $106.50   $106.50   $106.50  
  Purchase #3 $99.92   7.289%   $107.2032   $107.20   $107.20   $107.20  
  Purchase #4 $146.93   12.779%   $165.7062   $165.71   $165.70   $165.70  
  Purchase #5 $161.71   12.743%   $182.3167   $182.32   $182.30   $182.30  
  Purchase #6 $153.33   3.361%   $158.4834   $158.48   $158.50   $158.50  
  Purchase #7 $60.39   3.483%   $62.4934   $62.49   $62.50   $62.50  
  7 purchase totals = $743.21       $808.6892   $808.69   $808.70   $808.70