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 $49.63   12.214%   $55.6918   $55.69   $55.70   $55.70  
  Purchase #2 $229.49   8.445%   $248.8704   $248.87   $248.85   $248.90  
  Purchase #3 $185.47   11.685%   $207.1422   $207.14   $207.15   $207.10  
  Purchase #4 $166.76   5.413%   $175.7867   $175.79   $175.80   $175.80  
  Purchase #5 $175.76   5.687%   $185.7555   $185.76   $185.75   $185.80  
  Purchase #6 $118.97   6.853%   $127.123   $127.12   $127.10   $127.10  
  Purchase #7 $118.66   5.742%   $125.4735   $125.47   $125.45   $125.50  
  7 purchase totals = $1,044.74       $1,125.8431   $1,125.84   $1,125.80   $1,125.90