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 $136.51   11.763%   $152.5677   $152.57   $152.55   $152.60  
  Purchase #2 $197.44   6.841%   $210.9469   $210.95   $210.95   $210.90  
  Purchase #3 $154.33   12.871%   $174.1938   $174.19   $174.20   $174.20  
  Purchase #4 $153.75   6.622%   $163.9313   $163.93   $163.95   $163.90  
  Purchase #5 $16.94   4.109%   $17.6361   $17.64   $17.65   $17.60  
  Purchase #6 $121.75   13.566%   $138.2666   $138.27   $138.25   $138.30  
  Purchase #7 $210.41   5.274%   $221.507   $221.51   $221.50   $221.50  
  7 purchase totals = $991.13       $1,079.0494   $1,079.06   $1,079.05   $1,079.00