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 $52.51   11.307%   $58.4473   $58.45   $58.45   $58.40  
  Purchase #2 $214.87   8.423%   $232.9685   $232.97   $232.95   $233.00  
  Purchase #3 $45.57   11.596%   $50.8543   $50.85   $50.85   $50.90  
  Purchase #4 $161.30   10.793%   $178.7091   $178.71   $178.70   $178.70  
  Purchase #5 $185.27   8.527%   $201.068   $201.07   $201.05   $201.10  
  Purchase #6 $23.49   4.610%   $24.5729   $24.57   $24.55   $24.60  
  Purchase #7 $24.93   13.856%   $28.3843   $28.38   $28.40   $28.40  
  7 purchase totals = $707.94       $775.0044   $775.00   $774.95   $775.10