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 $223.41   11.659%   $249.4574   $249.46   $249.45   $249.50  
  Purchase #2 $120.93   3.388%   $125.0271   $125.03   $125.05   $125.00  
  Purchase #3 $191.64   7.230%   $205.4956   $205.50   $205.50   $205.50  
  Purchase #4 $245.52   8.598%   $266.6298   $266.63   $266.65   $266.60  
  Purchase #5 $192.63   6.767%   $205.6653   $205.67   $205.65   $205.70  
  Purchase #6 $57.75   6.212%   $61.3374   $61.34   $61.35   $61.30  
  Purchase #7 $231.29   6.227%   $245.6924   $245.69   $245.70   $245.70  
  7 purchase totals = $1,263.17       $1,359.3050   $1,359.32   $1,359.35   $1,359.30