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 $95.37   11.803%   $106.6265   $106.63   $106.65   $106.60  
  Purchase #2 $125.49   4.813%   $131.5298   $131.53   $131.55   $131.50  
  Purchase #3 $132.58   4.552%   $138.615   $138.62   $138.60   $138.60  
  Purchase #4 $77.68   9.667%   $85.1893   $85.19   $85.20   $85.20  
  Purchase #5 $24.93   10.773%   $27.6157   $27.62   $27.60   $27.60  
  Purchase #6 $8.76   8.576%   $9.5113   $9.51   $9.50   $9.50  
  Purchase #7 $98.34   9.318%   $107.5033   $107.50   $107.50   $107.50  
  7 purchase totals = $563.15       $606.5909   $606.60   $606.60   $606.50