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 $225.49   12.266%   $253.1486   $253.15   $253.15   $253.10  
  Purchase #2 $231.56   8.669%   $251.6339   $251.63   $251.65   $251.60  
  Purchase #3 $60.80   5.705%   $64.2686   $64.27   $64.25   $64.30  
  Purchase #4 $167.47   11.207%   $186.2384   $186.24   $186.25   $186.20  
  Purchase #5 $96.87   4.440%   $101.171   $101.17   $101.15   $101.20  
  Purchase #6 $184.99   4.820%   $193.9065   $193.91   $193.90   $193.90  
  Purchase #7 $74.72   11.814%   $83.5474   $83.55   $83.55   $83.50  
  7 purchase totals = $1,041.90       $1,133.9144   $1,133.92   $1,133.90   $1,133.80