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 $232.56   8.448%   $252.2067   $252.21   $252.20   $252.20  
  Purchase #2 $27.64   8.568%   $30.0082   $30.01   $30.00   $30.00  
  Purchase #3 $60.70   6.873%   $64.8719   $64.87   $64.85   $64.90  
  Purchase #4 $192.83   7.189%   $206.6925   $206.69   $206.70   $206.70  
  Purchase #5 $155.30   3.358%   $160.515   $160.52   $160.50   $160.50  
  Purchase #6 $106.35   3.337%   $109.8989   $109.90   $109.90   $109.90  
  Purchase #7 $249.63   8.730%   $271.4227   $271.42   $271.40   $271.40  
  7 purchase totals = $1,025.01       $1,095.6159   $1,095.62   $1,095.55   $1,095.60