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 $64.68   5.648%   $68.3331   $68.33   $68.35   $68.30  
  Purchase #2 $148.38   6.609%   $158.1864   $158.19   $158.20   $158.20  
  Purchase #3 $196.37   9.418%   $214.8641   $214.86   $214.85   $214.90  
  Purchase #4 $36.48   12.848%   $41.167   $41.17   $41.15   $41.20  
  Purchase #5 $68.90   9.622%   $75.5296   $75.53   $75.55   $75.50  
  Purchase #6 $225.57   12.610%   $254.0144   $254.01   $254.00   $254.00  
  Purchase #7 $79.71   7.871%   $85.984   $85.98   $86.00   $86.00  
  7 purchase totals = $820.09       $898.0786   $898.07   $898.10   $898.10