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 $136.73   13.598%   $155.3225   $155.32   $155.30   $155.30  
  Purchase #2 $61.87   8.247%   $66.9724   $66.97   $66.95   $67.00  
  Purchase #3 $250.79   6.560%   $267.2418   $267.24   $267.25   $267.20  
  Purchase #4 $181.53   13.798%   $206.5775   $206.58   $206.60   $206.60  
  Purchase #5 $126.45   11.584%   $141.098   $141.10   $141.10   $141.10  
  Purchase #6 $77.57   10.798%   $85.946   $85.95   $85.95   $85.90  
  Purchase #7 $93.98   4.402%   $98.117   $98.12   $98.10   $98.10  
  7 purchase totals = $928.92       $1,021.2752   $1,021.28   $1,021.25   $1,021.20