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 $138.67   11.464%   $154.5671   $154.57   $154.55   $154.60  
  Purchase #2 $248.92   4.704%   $260.6292   $260.63   $260.65   $260.60  
  Purchase #3 $179.94   12.742%   $202.868   $202.87   $202.85   $202.90  
  Purchase #4 $89.38   11.395%   $99.5649   $99.56   $99.55   $99.60  
  Purchase #5 $34.91   11.657%   $38.9795   $38.98   $39.00   $39.00  
  Purchase #6 $248.91   6.833%   $265.918   $265.92   $265.90   $265.90  
  Purchase #7 $207.40   13.105%   $234.5798   $234.58   $234.60   $234.60  
  7 purchase totals = $1,148.13       $1,257.1065   $1,257.11   $1,257.10   $1,257.20