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 $218.87   10.840%   $242.5955   $242.60   $242.60   $242.60  
  Purchase #2 $58.38   11.195%   $64.9156   $64.92   $64.90   $64.90  
  Purchase #3 $72.34   4.243%   $75.4094   $75.41   $75.40   $75.40  
  Purchase #4 $216.37   6.548%   $230.5379   $230.54   $230.55   $230.50  
  Purchase #5 $88.73   8.386%   $96.1709   $96.17   $96.15   $96.20  
  Purchase #6 $78.92   11.871%   $88.2886   $88.29   $88.30   $88.30  
  Purchase #7 $248.59   7.469%   $267.1572   $267.16   $267.15   $267.20  
  7 purchase totals = $982.20       $1,065.0751   $1,065.09   $1,065.05   $1,065.10