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 $247.81   5.331%   $261.0208   $261.02   $261.00   $261.00  
  Purchase #2 $57.97   6.450%   $61.7091   $61.71   $61.70   $61.70  
  Purchase #3 $117.40   8.721%   $127.6385   $127.64   $127.65   $127.60  
  Purchase #4 $152.98   9.669%   $167.7716   $167.77   $167.75   $167.80  
  Purchase #5 $98.69   12.775%   $111.2976   $111.30   $111.30   $111.30  
  Purchase #6 $27.50   9.270%   $30.0493   $30.05   $30.05   $30.00  
  Purchase #7 $118.29   11.586%   $131.9951   $132.00   $132.00   $132.00  
  7 purchase totals = $820.64       $891.4820   $891.49   $891.45   $891.40