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 $237.72   12.311%   $266.9857   $266.99   $267.00   $267.00  
  Purchase #2 $167.75   12.395%   $188.5426   $188.54   $188.55   $188.50  
  Purchase #3 $168.77   10.538%   $186.555   $186.56   $186.55   $186.60  
  Purchase #4 $214.55   3.498%   $222.055   $222.06   $222.05   $222.10  
  Purchase #5 $185.48   12.457%   $208.5852   $208.59   $208.60   $208.60  
  Purchase #6 $200.28   10.104%   $220.5163   $220.52   $220.50   $220.50  
  Purchase #7 $229.25   5.217%   $241.21   $241.21   $241.20   $241.20  
  7 purchase totals = $1,403.80       $1,534.4498   $1,534.47   $1,534.45   $1,534.50