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 $24.88   6.386%   $26.4688   $26.47   $26.45   $26.50  
  Purchase #2 $219.55   6.277%   $233.3312   $233.33   $233.35   $233.30  
  Purchase #3 $38.97   5.313%   $41.0405   $41.04   $41.05   $41.00  
  Purchase #4 $148.90   11.505%   $166.0309   $166.03   $166.05   $166.00  
  Purchase #5 $105.74   11.739%   $118.1528   $118.15   $118.15   $118.20  
  Purchase #6 $176.83   9.334%   $193.3353   $193.34   $193.35   $193.30  
  Purchase #7 $122.66   9.503%   $134.3164   $134.32   $134.30   $134.30  
  7 purchase totals = $837.53       $912.6759   $912.68   $912.70   $912.60