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 $192.46   11.147%   $213.9135   $213.91   $213.90   $213.90  
  Purchase #2 $214.64   8.421%   $232.7148   $232.71   $232.70   $232.70  
  Purchase #3 $215.68   4.243%   $224.8313   $224.83   $224.85   $224.80  
  Purchase #4 $212.96   3.662%   $220.7586   $220.76   $220.75   $220.80  
  Purchase #5 $202.93   9.487%   $222.182   $222.18   $222.20   $222.20  
  Purchase #6 $186.87   10.607%   $206.6913   $206.69   $206.70   $206.70  
  Purchase #7 $5.85   5.416%   $6.1668   $6.17   $6.15   $6.20  
  7 purchase totals = $1,231.39       $1,327.2583   $1,327.25   $1,327.25   $1,327.30