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 $45.79   8.564%   $49.7115   $49.71   $49.70   $49.70  
  Purchase #2 $244.36   9.186%   $266.8069   $266.81   $266.80   $266.80  
  Purchase #3 $17.31   9.319%   $18.9231   $18.92   $18.90   $18.90  
  Purchase #4 $178.97   11.141%   $198.909   $198.91   $198.90   $198.90  
  Purchase #5 $183.31   6.611%   $195.4286   $195.43   $195.45   $195.40  
  Purchase #6 $239.25   8.428%   $259.414   $259.41   $259.40   $259.40  
  Purchase #7 $58.31   13.715%   $66.3072   $66.31   $66.30   $66.30  
  7 purchase totals = $967.30       $1,055.5003   $1,055.50   $1,055.45   $1,055.40