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 $192.40   5.239%   $202.4798   $202.48   $202.50   $202.50  
  Purchase #2 $209.38   9.256%   $228.7602   $228.76   $228.75   $228.80  
  Purchase #3 $38.47   13.374%   $43.615   $43.62   $43.60   $43.60  
  Purchase #4 $116.75   5.745%   $123.4573   $123.46   $123.45   $123.50  
  Purchase #5 $92.87   3.188%   $95.8307   $95.83   $95.85   $95.80  
  Purchase #6 $50.46   5.153%   $53.0602   $53.06   $53.05   $53.10  
  Purchase #7 $106.64   13.615%   $121.159   $121.16   $121.15   $121.20  
  7 purchase totals = $806.97       $868.3622   $868.37   $868.35   $868.50