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 $48.76   8.693%   $52.9987   $53.00   $53.00   $53.00  
  Purchase #2 $155.85   12.720%   $175.6741   $175.67   $175.65   $175.70  
  Purchase #3 $196.30   6.623%   $209.3009   $209.30   $209.30   $209.30  
  Purchase #4 $151.94   3.562%   $157.3521   $157.35   $157.35   $157.40  
  Purchase #5 $163.73   7.537%   $176.0703   $176.07   $176.05   $176.10  
  Purchase #6 $30.51   6.624%   $32.531   $32.53   $32.55   $32.50  
  Purchase #7 $191.30   9.749%   $209.9498   $209.95   $209.95   $209.90  
  7 purchase totals = $938.39       $1,013.8769   $1,013.87   $1,013.85   $1,013.90