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 $174.61   9.699%   $191.5454   $191.55   $191.55   $191.50  
  Purchase #2 $241.69   8.114%   $261.3007   $261.30   $261.30   $261.30  
  Purchase #3 $136.29   7.592%   $146.6371   $146.64   $146.65   $146.60  
  Purchase #4 $228.99   8.240%   $247.8588   $247.86   $247.85   $247.90  
  Purchase #5 $61.81   8.476%   $67.049   $67.05   $67.05   $67.00  
  Purchase #6 $80.83   3.675%   $83.8005   $83.80   $83.80   $83.80  
  Purchase #7 $7.30   13.477%   $8.2838   $8.28   $8.30   $8.30  
  7 purchase totals = $931.52       $1,006.4753   $1,006.48   $1,006.50   $1,006.40