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 $182.66   13.108%   $206.6031   $206.60   $206.60   $206.60  
  Purchase #2 $129.32   5.516%   $136.4533   $136.45   $136.45   $136.50  
  Purchase #3 $94.45   11.462%   $105.2759   $105.28   $105.30   $105.30  
  Purchase #4 $121.60   6.217%   $129.1599   $129.16   $129.15   $129.20  
  Purchase #5 $188.83   13.747%   $214.7885   $214.79   $214.80   $214.80  
  Purchase #6 $245.29   9.209%   $267.8788   $267.88   $267.90   $267.90  
  Purchase #7 $186.85   10.454%   $206.3833   $206.38   $206.40   $206.40  
  7 purchase totals = $1,149.00       $1,266.5428   $1,266.54   $1,266.60   $1,266.70