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 $59.40   8.823%   $64.6409   $64.64   $64.65   $64.60  
  Purchase #2 $135.92   6.539%   $144.8078   $144.81   $144.80   $144.80  
  Purchase #3 $229.51   13.687%   $260.923   $260.92   $260.90   $260.90  
  Purchase #4 $48.95   8.712%   $53.2145   $53.21   $53.20   $53.20  
  Purchase #5 $88.69   4.403%   $92.595   $92.60   $92.60   $92.60  
  Purchase #6 $250.92   6.339%   $266.8258   $266.83   $266.85   $266.80  
  Purchase #7 $115.55   12.749%   $130.2815   $130.28   $130.30   $130.30  
  7 purchase totals = $928.94       $1,013.2885   $1,013.29   $1,013.30   $1,013.20