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 $55.91   12.573%   $62.9396   $62.94   $62.95   $62.90  
  Purchase #2 $139.44   6.623%   $148.6751   $148.68   $148.70   $148.70  
  Purchase #3 $227.97   6.183%   $242.0654   $242.07   $242.05   $242.10  
  Purchase #4 $230.44   12.671%   $259.6391   $259.64   $259.65   $259.60  
  Purchase #5 $163.69   9.279%   $178.8788   $178.88   $178.90   $178.90  
  Purchase #6 $33.30   3.487%   $34.4612   $34.46   $34.45   $34.50  
  Purchase #7 $115.29   4.204%   $120.1368   $120.14   $120.15   $120.10  
  7 purchase totals = $966.04       $1,046.7960   $1,046.81   $1,046.85   $1,046.80