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 $41.83   4.185%   $43.5806   $43.58   $43.60   $43.60  
  Purchase #2 $226.55   12.653%   $255.2154   $255.22   $255.20   $255.20  
  Purchase #3 $186.76   6.111%   $198.1729   $198.17   $198.15   $198.20  
  Purchase #4 $77.99   6.195%   $82.8215   $82.82   $82.80   $82.80  
  Purchase #5 $135.75   7.614%   $146.086   $146.09   $146.10   $146.10  
  Purchase #6 $192.38   10.468%   $212.5183   $212.52   $212.50   $212.50  
  Purchase #7 $118.94   8.187%   $128.6776   $128.68   $128.70   $128.70  
  7 purchase totals = $980.20       $1,067.0723   $1,067.08   $1,067.05   $1,067.10