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 $231.59   13.548%   $262.9658   $262.97   $262.95   $263.00  
  Purchase #2 $207.48   10.764%   $229.8131   $229.81   $229.80   $229.80  
  Purchase #3 $115.56   10.461%   $127.6487   $127.65   $127.65   $127.60  
  Purchase #4 $190.50   4.193%   $198.4877   $198.49   $198.50   $198.50  
  Purchase #5 $187.87   9.400%   $205.5298   $205.53   $205.55   $205.50  
  Purchase #6 $187.48   13.586%   $212.951   $212.95   $212.95   $213.00  
  Purchase #7 $13.69   4.246%   $14.2713   $14.27   $14.25   $14.30  
  7 purchase totals = $1,134.17       $1,251.6674   $1,251.67   $1,251.65   $1,251.70