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 $119.76   6.682%   $127.7624   $127.76   $127.75   $127.80  
  Purchase #2 $27.38   12.355%   $30.7628   $30.76   $30.75   $30.80  
  Purchase #3 $238.71   5.250%   $251.2423   $251.24   $251.25   $251.20  
  Purchase #4 $233.54   8.188%   $252.6623   $252.66   $252.65   $252.70  
  Purchase #5 $181.59   6.707%   $193.7692   $193.77   $193.75   $193.80  
  Purchase #6 $226.61   4.663%   $237.1768   $237.18   $237.20   $237.20  
  Purchase #7 $103.67   5.398%   $109.2661   $109.27   $109.25   $109.30  
  7 purchase totals = $1,131.26       $1,202.6419   $1,202.64   $1,202.60   $1,202.80