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 $216.69   13.286%   $245.4794   $245.48   $245.50   $245.50  
  Purchase #2 $120.35   3.615%   $124.7007   $124.70   $124.70   $124.70  
  Purchase #3 $160.87   4.704%   $168.4373   $168.44   $168.45   $168.40  
  Purchase #4 $180.39   10.158%   $198.714   $198.71   $198.70   $198.70  
  Purchase #5 $9.90   9.838%   $10.874   $10.87   $10.85   $10.90  
  Purchase #6 $208.41   12.642%   $234.7572   $234.76   $234.75   $234.80  
  Purchase #7 $82.85   13.709%   $94.2079   $94.21   $94.20   $94.20  
  7 purchase totals = $979.46       $1,077.1705   $1,077.17   $1,077.15   $1,077.20