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 $234.96   11.468%   $261.9052   $261.91   $261.90   $261.90  
  Purchase #2 $119.64   5.568%   $126.3016   $126.30   $126.30   $126.30  
  Purchase #3 $142.57   3.728%   $147.885   $147.89   $147.90   $147.90  
  Purchase #4 $184.69   3.452%   $191.0655   $191.07   $191.05   $191.10  
  Purchase #5 $68.70   13.427%   $77.9243   $77.92   $77.90   $77.90  
  Purchase #6 $222.93   11.763%   $249.1533   $249.15   $249.15   $249.20  
  Purchase #7 $190.32   5.598%   $200.9741   $200.97   $200.95   $201.00  
  7 purchase totals = $1,163.81       $1,255.2090   $1,255.21   $1,255.15   $1,255.30