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 $38.90   9.683%   $42.6667   $42.67   $42.65   $42.70  
  Purchase #2 $12.31   5.512%   $12.9885   $12.99   $13.00   $13.00  
  Purchase #3 $29.27   4.611%   $30.6196   $30.62   $30.60   $30.60  
  Purchase #4 $235.40   3.118%   $242.7398   $242.74   $242.75   $242.70  
  Purchase #5 $236.79   6.748%   $252.7686   $252.77   $252.75   $252.80  
  Purchase #6 $54.63   8.172%   $59.0944   $59.09   $59.10   $59.10  
  Purchase #7 $96.52   7.823%   $104.0708   $104.07   $104.05   $104.10  
  7 purchase totals = $703.82       $744.9484   $744.95   $744.90   $745.00