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 $228.85   12.214%   $256.8017   $256.80   $256.80   $256.80  
  Purchase #2 $32.29   13.358%   $36.6033   $36.60   $36.60   $36.60  
  Purchase #3 $177.28   9.704%   $194.4833   $194.48   $194.50   $194.50  
  Purchase #4 $124.58   9.684%   $136.6443   $136.64   $136.65   $136.60  
  Purchase #5 $164.91   9.312%   $180.2664   $180.27   $180.25   $180.30  
  Purchase #6 $159.69   7.670%   $171.9382   $171.94   $171.95   $171.90  
  Purchase #7 $63.46   8.777%   $69.0299   $69.03   $69.05   $69.00  
  7 purchase totals = $951.06       $1,045.7671   $1,045.76   $1,045.80   $1,045.70