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 $247.64   11.709%   $276.6362   $276.64   $276.65   $276.60  
  Purchase #2 $64.52   4.545%   $67.4524   $67.45   $67.45   $67.50  
  Purchase #3 $186.72   8.371%   $202.3503   $202.35   $202.35   $202.40  
  Purchase #4 $202.40   12.448%   $227.5948   $227.59   $227.60   $227.60  
  Purchase #5 $13.40   3.562%   $13.8773   $13.88   $13.90   $13.90  
  Purchase #6 $156.56   3.361%   $161.822   $161.82   $161.80   $161.80  
  Purchase #7 $108.34   10.667%   $119.8966   $119.90   $119.90   $119.90  
  7 purchase totals = $979.58       $1,069.6296   $1,069.63   $1,069.65   $1,069.70