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 $113.43   4.315%   $118.3245   $118.32   $118.30   $118.30  
  Purchase #2 $229.96   13.828%   $261.7589   $261.76   $261.75   $261.80  
  Purchase #3 $186.43   8.464%   $202.2094   $202.21   $202.20   $202.20  
  Purchase #4 $157.57   13.264%   $178.4701   $178.47   $178.45   $178.50  
  Purchase #5 $211.31   7.277%   $226.687   $226.69   $226.70   $226.70  
  Purchase #6 $230.47   9.432%   $252.2079   $252.21   $252.20   $252.20  
  Purchase #7 $107.91   13.334%   $122.2987   $122.30   $122.30   $122.30  
  7 purchase totals = $1,237.08       $1,361.9565   $1,361.96   $1,361.90   $1,362.00