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 $57.91   9.353%   $63.3263   $63.33   $63.35   $63.30  
  Purchase #2 $225.78   5.274%   $237.6876   $237.69   $237.70   $237.70  
  Purchase #3 $161.64   10.524%   $178.651   $178.65   $178.65   $178.70  
  Purchase #4 $140.49   3.745%   $145.7514   $145.75   $145.75   $145.80  
  Purchase #5 $102.56   6.676%   $109.4069   $109.41   $109.40   $109.40  
  Purchase #6 $70.54   3.505%   $73.0124   $73.01   $73.00   $73.00  
  Purchase #7 $175.25   13.334%   $198.6178   $198.62   $198.60   $198.60  
  7 purchase totals = $934.17       $1,006.4534   $1,006.46   $1,006.45   $1,006.50