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 $69.32   12.149%   $77.7417   $77.74   $77.75   $77.70  
  Purchase #2 $22.86   13.210%   $25.8798   $25.88   $25.90   $25.90  
  Purchase #3 $159.64   6.252%   $169.6207   $169.62   $169.60   $169.60  
  Purchase #4 $236.35   5.170%   $248.5693   $248.57   $248.55   $248.60  
  Purchase #5 $161.44   12.774%   $182.0623   $182.06   $182.05   $182.10  
  Purchase #6 $130.49   12.149%   $146.3432   $146.34   $146.35   $146.30  
  Purchase #7 $134.70   10.457%   $148.7856   $148.79   $148.80   $148.80  
  7 purchase totals = $914.80       $999.0026   $999.00   $999.00   $999.00