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 $192.59   6.704%   $205.5012   $205.50   $205.50   $205.50  
  Purchase #2 $49.72   9.602%   $54.4941   $54.49   $54.50   $54.50  
  Purchase #3 $145.35   7.791%   $156.6742   $156.67   $156.65   $156.70  
  Purchase #4 $98.69   7.475%   $106.0671   $106.07   $106.05   $106.10  
  Purchase #5 $8.48   6.569%   $9.0371   $9.04   $9.05   $9.00  
  Purchase #6 $154.67   9.872%   $169.939   $169.94   $169.95   $169.90  
  Purchase #7 $232.65   10.838%   $257.8646   $257.86   $257.85   $257.90  
  7 purchase totals = $882.15       $959.5773   $959.57   $959.55   $959.60