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 $242.80   10.130%   $267.3956   $267.40   $267.40   $267.40  
  Purchase #2 $153.39   5.336%   $161.5749   $161.57   $161.55   $161.60  
  Purchase #3 $212.72   4.497%   $222.286   $222.29   $222.30   $222.30  
  Purchase #4 $226.71   11.498%   $252.7771   $252.78   $252.80   $252.80  
  Purchase #5 $159.60   9.774%   $175.1993   $175.20   $175.20   $175.20  
  Purchase #6 $102.97   8.471%   $111.6926   $111.69   $111.70   $111.70  
  Purchase #7 $6.95   11.611%   $7.757   $7.76   $7.75   $7.80  
  7 purchase totals = $1,105.14       $1,198.6825   $1,198.69   $1,198.70   $1,198.80