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 $23.27   12.821%   $26.2534   $26.25   $26.25   $26.30  
  Purchase #2 $174.54   4.824%   $182.9598   $182.96   $182.95   $183.00  
  Purchase #3 $186.85   11.600%   $208.5246   $208.52   $208.50   $208.50  
  Purchase #4 $42.74   6.457%   $45.4997   $45.50   $45.50   $45.50  
  Purchase #5 $33.74   3.182%   $34.8136   $34.81   $34.80   $34.80  
  Purchase #6 $227.76   4.288%   $237.5263   $237.53   $237.55   $237.50  
  Purchase #7 $182.70   12.866%   $206.2062   $206.21   $206.20   $206.20  
  7 purchase totals = $871.60       $941.7836   $941.78   $941.75   $941.80