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 $204.71   7.129%   $219.3038   $219.30   $219.30   $219.30  
  Purchase #2 $60.61   10.863%   $67.1941   $67.19   $67.20   $67.20  
  Purchase #3 $77.36   4.870%   $81.1274   $81.13   $81.15   $81.10  
  Purchase #4 $158.76   13.863%   $180.7689   $180.77   $180.75   $180.80  
  Purchase #5 $227.69   12.493%   $256.1353   $256.14   $256.15   $256.10  
  Purchase #6 $165.47   12.284%   $185.7963   $185.80   $185.80   $185.80  
  Purchase #7 $204.45   4.796%   $214.2554   $214.26   $214.25   $214.30  
  7 purchase totals = $1,099.05       $1,204.5812   $1,204.59   $1,204.60   $1,204.60